Summary
The external urethral sphincter (EUS) and external anal sphincter (EAS) are striated muscles that function to maintain urinary and fecal continence respectively. This study examines the short-latency synaptic input from a variety of cutaneous perineal and muscle/cutaneous hindlimb afferents to the motoneurons innervating these muscles. Intracellular recordings from anti dromically identified EUS and EAS motoneurons provided records of the postsynaptic potentials (PSPs) produced by electrical stimulation of peripheral afferents in decerebrate or chloralose anesthetized cats. Excitatory postsynaptic potentials (EPSPs) were produced in most EUS and EAS motoneurons by stimulation of ipsilateral and contralateral sensory pudendal (SPud) and superficial perineal (SPeri) cutaneous nerves. The shortest cen tral latencies in the study (1.5 ms) suggest that there are disynaptic excitatory, in addition to tri-and oligosynap tic, connections within these reflex pathways. EPSPs mixed with longer latency inhibitory potentials (E/I PSPs) were observed in both motoneuron populations but were found more frequently in EAS motoneurons. These E/I PSPs were evoked more often from contralat eral afferents than from ipsilateral afferents. Cutaneous nerves innervating the hindlimb had weaker if any synaptic effects on sphincter motoneurons. Stimulation of ipsilateral hindlimb muscle nerves rarely produced PSPs in EUS motoneurons and had weak synaptic actions on EAS motoneurons. In 2 of 22 animals (both decerebrate), large inhibitory potentials predominated over early small EPSPs suggesting that inhibitory pathways from these afferents to sphincter motoneurons can be released under certain circumstances. The relation between the segmental afferents to EUS and EAS motoneurons and the neural circuitry influencing them during micturition and defecation are discussed.
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References
Barrington FJF (1925) The effect of lesions of the hind- and mid-brain on micturition in the cat. Q J Exp Physiol 15: 81–102
Bishop A (1959) Reflex activity of external anal sphincter of cat. J Neurophysiol 22: 679–692
Bishop B, Garry RC, Roberts TDM, Todd JK (1956) Control of the external sphincter of the anus in the cat. J Physiol 134: 229–240
Bradley WE, Teague CT (1977) Synaptic events in pudendal motoneurons of the cat. Exp Neurol 56: 237–240
deGroat WC (1990) Central neural control of the lower urinary tract. In: Bock G, Whelan J (eds) Neurobiology of incontinence. Ciba Foundation Symposium 151:27–56
deGroat WC, Booth AM, Krier J, Milne RJ, Morgan C, Nadelhaft I (1979) Neural control of the urinary bladder and large intestine. In: McCBrooks C, Koizumi K, Sato A (eds) Integrative functions of the autonomic nervous system. University of Tokyo Press Tokyo, pp 50–67
deGroat WC, Nadelhaft I, Milne RJ, Booth AM, Morgan C, Thor E (1981) Organization of the sacral parasympathetic reflex pathways to the urinary bladder and large intestine. J Auton Nerv Sys 3: 135–160
Dubrovsky B, Filipini D (1990) Neurobiological aspects of the pelvic floor muscles involved in defecation. Neurosci Biobehav Rev 14: 157–168
Eccles RM, Lundberg A (1959) Synaptic actions in motoneurones by afferents which may evoke the flexion reflex. Arch Ital Biol 97: 199–221
Edgley SA, Wallace NA (1989) A short-latency crossed pathway from cutaneous afferents to rat hindlimb motoneurons. J Physiol 411: 469–480
Fedirchuk B, Hochman H, Shefchyk SJ (1990) Synaptic inputs onto pudendal motoneurons from sacral segmental and brainstem pathways in the cat. Soc Neurosci Abstr 48 10
Fedirchuk B, Shefchyk SJ (1991) Effects of electrical stimulation of the thoracic spinal cord on bladder and external urethral sphincter activity in the decerebrate cat. Exp Brain Res 84: 635–642
Fedirchuk B, Song L, Downie JW, Shefchyk SJ (1992) Spinal distribution of extracellular field potentials generated by electrical stimulation of pudendal and perineal afferents in the cat. Exp Brain Res 89: 517–520
Fleshman JW, Lev-Tov A, Burke RE (1984) Peripheral and central control of flexor digitorum longus and flexor hallucis longus motoneurons: the synaptic basis of functional diversity. Exp Brain Res 54: 133–149
Fu TC, Santini M, Schomburg ED (1974) Characteristics and distribution of spinal focal synaptic potentials generated by group II muscle afferents. Acta Physiol Scand 91: 298–313
Fu TC, Schomburg ED (1974) Electrophysiological investigation of the projection of secondary muscle spindle afferents in the cat spinal cord. Acta Physiol Scand 91: 314–329
Fukuda H, Fukai K (1986) Location of the reflex centre for straining elicited by activation of pelvic afferent fibres of decerebrate dogs. Brain Res 380: 287–296
Garry RC, Roberts TDM, Todd JK (1959) Reflexes involving the external urethral sphincter in the cat. J Physiol 149: 653–665
Hochman S, Fedirchuk B, Shefchyk SJ (1991) Membrane electrical properties of external urethral and external anal sphincter somatic motoneurons in the decerebrate cat. Neurosci Lett 127: 87–90
Holstege G, Griffiths D, deWall H, Dalm E (1986) Anatomical and physiological observations on supraspinal control of bladder and urethral sphincter muscles in the cat. J Comp Neurol 250: 449–461
Hongo T, Jankowska E, Lundberg A (1969) The rubrospinal tract. I. Effects on alpha-motoneurones innervating hindlimb muscles in cats. Exp Brain Res 7: 344–364
Hursh JB (1939) Conduction velocity and diameter of nerve fibers. Am J Physiol 127: 131–139
Illert M, Lundberg A, Tanaka R (1975) Integration in a disynaptic cortico-motoneuronal pathway to the forelimb in the cat. Brain Res 93: 525–529
Jankowska E, Padel Y, Zarzecki P (1978) Crossed disynaptic inhibition of sacral motoneurones. J Physiol 285: 425–444
Jolesz FA, Cheng-Tao X, Ruenzel PW, Henneman E (1982) Flexor reflex control of the external sphincter of the urethra in paraplegia. Science 216: 1243–1245
Koyanagi T, Arikado K, Takamatsu T, Tsujui I (1982) Experience with electromyography of the external urethral sphincter in spinal cord injury patients. J Urol 127: 271–276
Kruse MN, Mallory BS, Noto H, Roppolo JR, deGroat WC (1991) Properties of the descending limb of the spinobulbospinal micturition reflex pathway in the cat. Brain Res 556: 6–12
Lundberg A (1975) Control of spinal mechanisms from the brain. In: Tower DB (ed) The nervous system, Vol. 1. The basic neurosciences. Raven Press, New York, pp 253–265
Mackel R (1979) Segmental and descending control of the external urethral and anal sphincters in the cat. J Physiol 294: 105–122
Martin WD, Fletcher TF, Bradley WE (1974) Innervation of feline perineal musculature. Anat Rec 180: 15–30
McMahon SB, Morrison JFB (1982) Factors that determine the excitability of parasympathetic reflexes to the cat bladder. J Physiol 322: 35–43
Omeniuk D (1990) Synaptic effects from cutaneous afforents in alpha motoneurons. Doctoral Thesis No 9020311, George Washington University, Washington D.C.
Pedersen E, Harving H, Klemar B, Torring J (1978) Human anal reflexes. J Neurol Neurosurg Psychiat 41: 813–818
Sasaki M (1991) Membrane properties of external urethral and external anal sphincter motoneurones in the cat. J Physiol 440: 345–366
Shefchyk SJ (1989) The effects of lumbosacral deafferentation on pontine micturition centre-evoked voiding in the decerebrate cat. Neurosci Lett 99: 175–180
Thor KB, Hisamitsu T, deGroat WC (1990) Unmasking of a new somatovesical reflex in adult cats by the serotonin autoreceptor agonist 5-methoxy-N,N-dimethyltryptamine. Dev Brain Res 54: 35–42
Thor K, Kawatani M, deGroat WC (1986) Plasticity in the reflex pathways to the lower urinary tract of the cat during postnatal development and following spinal cord injury. In: Goldberger ME, Gorio A, Murray M (eds) Development and Plasticity of the mammalian spinal cord. Fidia Research Series, Vol. 3, Sect 2. pp 65–80
Vodusek DB, Janko M (1990) The bulbocavernosus reflex: a single motor neuron study. Brain 113: 813–820
Vodusek DB, Janko M, Lokar J (1983) Direct and reflex responses in perineal muscles on electrical stimulation. J Neurol Neurosurg Psychiat 46: 67–71
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Fedirchuk, B., Hochman, S. & Shefchyk, S.J. An intracellular study of perineal and hindlimb afferent inputs onto sphincter motoneurons in the decerebrate cat. Exp Brain Res 89, 511–516 (1992). https://doi.org/10.1007/BF00229875
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DOI: https://doi.org/10.1007/BF00229875