Effects on reflex bladder activity of chemical stimulation of small diameter afferents from skeletal muscle in the cat

The influence of afferent inputs from skin and viscera on the activity of the bladder and the skeletal muscle surrounding the urethra in the rat

(1) Somato-visceral and viscero-visceral reflex interactions have been studied in the bladder branches of the pelvic nerve and in the electromyographic (EMG) activity of the periurethral skeletal muscles of the anesthetized rat, and by observations of changes in bladder motility. (2) Slow distensions of the bladder caused some elevation of intravesical pressure, and culminated in a micturition contraction. Periurethral EMG activity increased gradually during the bladder distension, and showed an oscillatory marked increase during the bladder contraction. There was a small increase in pelvic nerve efferent activity during slow distension, and there was a substantial increase before, or at the start, of a micturition contraction. (3) Oscillatory bursting activity occurred in recordings of the EMG activity from periurethral skeletal muscle during the rising phase of micturition contraction; this was particularly so during the most rapid rise in intravesical pressure, and periods of electrical silence lasting 80-270 ms alternated with bursts of activity in the periurethral EMG. (4) In the present experiments, the switching mechanism activated by pelvic afferent signals related to intravesical pressure reversed the behavior of a number of reflex pathways. When the bladder pressure was low, nociceptive pinching of the perineal skin usually caused bladder contraction and a rise in pelvic nerve efferent activity and in periurethral EMG activity. When the bladder was full, micturition contractions were present and reduced in size and frequency by pinching of the perineal skin. The pelvic nerve efferent activity was correspondingly reduced, while the EMG activity increased during and following the nociceptive stimulus. Cooling the scrotal skin with ice also decreased the frequency of bladder contractions. (5) When the bladder pressure was low, distension of the anus and colon increased periurethral EMG activity, but did not affect bladder tone. However, when the bladder was full, these stimuli reduced the size and frequency of bladder contractions, associated with a reduction in the pelvic nerve efferent activity. There was usually a simultaneous reduction in the EMG activity in periurethral muscles. Similar results were obtained during distension of the seminal vesicles or vagina, or following injection of 20-60 microliters of saline into the lumen of the vas deferens. Reversal of the responses at extremes of intravesical pressure was observed in every case. (6) Following spinal transection at the upper cervical or thoracic level, micturition contractions were absent at high bladder volumes. However the effects described when the neuraxis was intact and the bladder pressure was low were still observed.(ABSTRACT TRUNCATED AT 400 WORDS)

Mechanism of the reflex inhibition of micturition contractions of the urinary bladder elicited by acupuncture-like stimulation in anesthetized rats

The effects of acupuncture-like stimulation of various segmental areas on the rhythmic micturition contractions (RMCs) of the urinary bladder were examined in anesthetized rats. The urinary bladder was cannulated via the urethra and expanded by infusing saline until the urinary bladder produced micturition contractions rhythmically as a consequence of the rhythmic burst discharges of the vesical pelvic efferent nerves. An acupuncture needle, having a diameter of either 160 or 340 microns, was inserted to a depth of about 4-5 mm into the skin and underlying muscles at various segmental areas, rostrally from the face then caudally to the hindlimb. Once being inserted, the needle was twisted left and right with the fingers about once every second for 1 min. (1) Acupuncture-like stimulation applied to the perineal area inhibited both the RMCs and the rhythmic burst discharges of vesical pelvic efferent nerves without any significant changes in the hypogastric efferent nerve activity. By contrast, stimulation applied to the face, neck, forelimb, chest, abdomen, back, and hindlimb areas was ineffective. (2) After surgically separating the perineal skin from the underlying muscles with the main cutaneous nerve branches intact, stimulation of either the perineal skin or the perineal muscles inhibited the RMCs. Stimulation of the perineal muscles produced a stronger inhibition of the RMCs than that of the perineal skin. (3) Stimulation of the perineal area increased afferent nerve activity, either recorded from the pudendal nerve branches innervating the perineal skin or underlying muscles, or recorded from the pelvic nerve branches innervating the perineal muscles. (4) The stimulation-induced inhibition of the RMCs was abolished after surgically severing both pudendal and pelvic nerve branches that innervated the perineal skin and underlying muscles. (5) The present findings indicate that the inhibition of the RMCs following acupuncture-like stimulation of the perineal area is a reflex response characterized by segmental organization. The afferent arcs of the reflex are both pelvic and pudendal nerve branches innervating the perineal skin and underlying muscles, while the efferent arcs are pelvic nerve branches innervating the urinary bladder.

Somato-vesical reflexes in chronic spinal cats

The effects of afferent volleys in hindlimb cutaneous and muscle nerves on vesical tone and contractility and on the discharges in pelvic nerves to the bladder were measured in anesthetized CNS-intact and 2-19 months chronic spinal cats. In chronic spinal cats volleys in group III and IV fibers increased the tone of the quiet, empty bladder (excitatory somato-vesical reflex). The same volleys inhibited the slow, large, rhythmic micturition contractions of the expanded bladder (inhibitory somato-vesical reflex). In CNS intact cats single or short tetanic volleys induced a reflex discharge in pelvic vesical nerve branches with 3 distinct components. These reflexes could be observed during micturition contractions, not markedly between the contractions or when the bladder was empty and quiet. The latencies of the 3 components were 90, 320 and 770 ms, respectively. The two early components (AI- and A2-reflex) were evoked by volleys in group II and III hindlimb afferents. The late component (C-reflex) was induced by group IV volleys. In chronic spinal cats a group II and III-induced A-reflex (latency 90 ms) and a group IV-induced C-reflex (latency 340 ms) were observed. The central pathways and the physiological significance of the various somato-vesical reflexes are discussed.

Changes in heart rate and blood pressure upon injection of algesic agents into skeletal muscle

In cats anaesthetized with chloralose and urethane algesic substances were injected intra-arterially into muscles of the left hindlimb and the resulting changes in heart rate and blood pressure recorded. The vagus nerves and both carotid sinus nerves were cut. Injection of KCl regularly induces acceleration of the heart rate and an increase in blood pressure. With bradykinin both accelerations and decelerations were observed (with or without accompanying pressor or depressor responses respectively). Injection of serotonin was rather ineffective in producing heart rate or blood pressure changes but subsequent injections of either KCl or bradykinin gave rise to enhanced acceleration and pressor responses. In the discussion it will be proposed that the diverse responses are due to differences in the composition of the afferent volleys elicited, probably because besides stimulating nociceptors these algesic substances activate to a varying extent non-nociceptive muscular fine afferent units of different modality and various central actions.

Factors that determine the excitability of parasympathetic reflexes to the cat bladder

1. Spino-bulbo-spinal reflex responses could be recorded from the vesical branches of the pelvic nerve following electrical stimulation of afferents in the vesical or colonic branches of the pelvic nerves, the hypogastric or pudendal nerves. The latencies of responses from these different sources were similar.2. Short latency responses could be recorded from the vesical branches of the pelvic nerve on electrical stimulation of descending pathways in the spinal cord and ipsilateral to and just below a hemitransection at the second cervical segment.3. These responses were facilitated by increases in intravesical pressure, maximal facilitation occurring at about 30 mmHg. Conversely, increases in intracolonic pressure inhibited these parasympathetic evoked responses, the maximum effect being seen with intracolonic pressures of 40-50 mmHg.4. These results suggest that the spino-bulbo-spinal responses that are recorded from the vesical parasympathetic efferents can be elicited from nerves innervating viscera other than the bladder, and also somatic structures. The effects of these spino-bulbo-spinal pathways on vesical parasympathetic efferents are dependent on antagonistic influences of intravesical and intracolonic pressure.5. The pathways that mediate the changes in excitability in these reflexes appear to act at least in part at the termination of the bulbo-spinal limb of the reflex, and involve afferents in the pelvic nerves but not the hypogastric or lumbar colonic nerves.6. It is proposed that the neurones that mediate this ;gating' action on the excitability of pelvic nerve reflexes are located in the sacral cord, and form a proportion of the population of interneurones described by McMahon & Morrison (1982b). In addition it is proposed that the neurones which mediate the ascending limb of the spino-bulbo-spinal reflexes are the long ascending neurones described by McMahon & Morrison (1982a).

Spinal neurones with long projections activated from the abdominal viscera of the cat

1. Recordings have been made from seventy-three neurones responding to electrical stimulation of pelvic, hypogastric or lumbar colonic nerves, in decerebrate or anaesthetized cats. Fifty-two of the units had long projections that ascended to the first cervical segment, and no units with visceral inputs were found to belong to the spino-cervical tract. Twenty-one units had long descending projections.2. Twenty percent (i.e. 11/46) responded to parasympathetic (pelvic) nerve stimulation (group 1) whilst 80% (35/46) responded to stimulation of hypogastric and/or lumbar colonic nerves (group 2). Ninety percent of group 2 neurones also responded to pelvic nerve stimulation.3. The electrical thresholds for activation of the units indicated that the largest peripheral nerve fibres responsible for the response were of the Adelta size.4. Thirty-one of the neurones had visceral mechanosensitive receptive fields; twenty-one had simple receptive fields in the bladder (seven) or in the colon (fourteen), ten units had compound receptive fields. The response of units with simple receptive fields to mechanical stimulation were either inhibitory or excitatory, and slowly adapting or rapidly adapting. Forty-two units appeared to have no visceral mechano-sensitive receptive fields in spite of showing responses to visceral nerve stimulation.5. Fifty percent of the units tested responded to innocuous somatic stimuli, mostly derived from muscle or joint receptors. Some of the units were found to respond to injections of bradykinin (10-15 mug) into a hindlimb artery.6. Group 1 had predominantly inhibitory visceral receptive fields, and somatic receptive fields in structures innervated from sacral segments of the spinal cord. Group 2 units all received inputs from visceral nerves entering the spinal cord over lumbar segments; many also received projections from sacral segmental inputs. These inputs showed an equal mixture of excitatory and inhibitory visceral receptive fields and convergence from somatic inputs arising from lumbar as well as sacral dermatomes. It seems likely that this group represents units originating in lumbar as well as sacral segments of the cord.7. The possible role of these neurones as mediators of visceral sensations and visceral reflexes is discussed.

Heart rate changes reflecting modifications of efferent cardiac sympathetic outflow by cutaneous and muscle afferent volleys

In cats anesthetized with chloralose and urethane graded electrical stimulation of cutaneous and muscle nerves of the fore- and hindlimb was performed and the resulting changes in heart rate and blood pressure were recorded. The vagus nerves were cut and the right carotid artery was tied off. The left carotid sinus was intact. Repetitive stimulation of cutaneous group II afferents did not change the heart rate nor the blood pressure. Cutaneous group III afferent activity led to an increased heart rate in about 70% of all trials. Very consistent increases in heart rate were always seen when repetitive group IV cutaneous volleys were elicited. Volleys in group I and II muscle afferents were ineffective. With group III muscle volleys bradycardiac (in about 40% of all trials) or tachycardiac (in about 30%) responses were observed. The nature of the response depended on the experimental situation but was difficult to predict or to modify. Stimulation of group IV muscle afferents always induced definite increases in heart rate. The latency for the onset of the heart rate changes was of the order of 3--10 s, and the time of peak during prolonged stimulation was about 20--30 s. There was a marked early and a small late response adaptation during prolonged repetitive stimulation, but the control heart rate was only reached some 40--65 s after the end of the stimulation. For group IV volleys the minimal effective frequency of the repetitive stimulation was between 0.25 and 1.0 Hz, the optimal one between 6 and 15 Hz. At higher stimulus frequencies a decline of the responses was observed. At the optimal frequency about 5 volleys were sufficient to induce a just detectable heart rate change. Mainly from the results obtained with group III fiber stimulation it is concluded that the intensity and direction of somatically induced heart rate changes are not strictly related to the afferent fiber groups (i.e. fiber threshold and diameter), as suggested by the concept of "pressor" and "depressor" nerve fibers, but to the modality of the receptive units which the fibers subserve.

Location and morphology of parasympathetic preganglionic neurons in the sacral spinal cord of the cat revealed by retrograde axonal transport of horseradish peroxidase

The distribution and morphology of preganglionic neurons in the sacral parasympathetic nucleus (SPN) of the cat have been studied with the horseradish peroxidase (HRP) tracing technique. HRP applied to the cut pelvic nerve was identified in cells located ipsilaterally, primarily in the intermediate gray matter. They formed a column approximately 10 mm long, usually contained within two, but occasionally three, sacral segments, S2 contained a majority of cells. In transverse sections the SPN had the appearance of an inverted "L". Cells were medium-sized, oval or spindle-shaped, and transversely oriented. They were distributed among two major components and one minor one: (1) dorsal band (34%) located mainly in lamina V beneath the dorsal horn (cells and dendrites horizontally oriented), (2) lateral band (64%) along the lateral edge of the gray matter in laminae VII through V (cells oriented dorsoventrally with dendrites extending within the nucleus and into the dorsolateral funiculus), and (3) a small group (2%) of cells at the rostral end of the SPN in lamina VII in the middle of the ventral horn. These data coupled with the results of other investigations indicate that the SPN has a viscerotopic organization wherein the colon is innervated primarily by cells in the dorsal band and the urinary bladder is innervated primarily by cells in the lateral band.

Reflex bladder activity induced by electrical stimulation of hind limb somatic afferents in the cat

Methods used and results obtained in a study of reflex responses of the bladder were as follows. Intravesical pressure was recorded continuously by the balloon method in chloralose--urethane anaesthetized cats. Various afferent fibres of hind limb cutaneous and muscle nerves were stimulated electrically, and the resulting changes in vesical functions were examined. It was found that: (1) when the bladder was nearly empty and quiescent, repetitive stimulation of group III (thin myelinated) and IV (non-myelinated) cutaneous or muscle afferent fibres of hind limb nerves caused a reflex increase in the vesical tonus. This somato-vesical excitatory reflex was propriospinal with its efferent are mainly in the pelvic nerves; (2) when there were spontaneous, large (amplitude above 300--400 mm H2O), rhythmic (about 1.0--2.5/min) micturition contractions of the expanded bladder, these contractions were inhibited by repetitive stimulation of the group III and IV cutaneous or muscle afferent fibres of hind limb nerves. The inhibition was sometimes followed by subsequent larger micturition contractions. The efferent arc for this somato-vesical inhibitory reflex was also in the pelvic nerves. Supraspinal structures were essential for producing the micturition contractions; (3) stimulation of group III and IV afferent fibres together was more effective than stimulation of the group III afferent fibres alone in activating either the excitatory or inhibitory somato-vesical reflex pathways.