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  • 1
    Electronic Resource
    Electronic Resource
    Evidence for a strychnine-sensitive mechanism and glycine receptors involved in the control of urethral sphincter activity during micturition in the cat (1998)
    Springer
    Experimental brain research 119 (1998), S. 297-306 
    Details
    ISSN: 1432-1106
    Keywords: Key words Spinal inhibition ; Interneurons ; Micturition ; Bladder-sphincter dyssynergia ; Cat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002210050345
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  • 2
    Electronic Resource
    Electronic Resource
    The role of Renshaw cells in locomotion: antagonism of their excitation from motor axon collaterals with intravenous mecamylamine (1987)
    Springer
    Experimental brain research 66 (1987), S. 99-105 
    Details
    ISSN: 1432-1106
    Keywords: Fictive locomotion ; Renshaw cells ; Mecamylamine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The contribution of Renshaw cell (RC) activity to the production of fictive locomotion in the mesencephalic preparation was examined using the nicotinic antagonist mecamylamine (MEC). After the i.v. administration of 3 doses of MEC (1.0 mg/kg) the following observations were made: 1) ventral root (VR) evoked discharge of RCs was decreased by up to 87.7%, 2) recurrent inhibitory postsynaptic potentials recorded in alpha motoneurons were greatly reduced or abolished, and 3) the rhythmic firing of RCs during the fictive step cycle was abolished in 83% of the cells examined. Locomotor drive potentials (LDPs) in motoneurons persisted during the fictive step cycle after MEC administration. Bursts of motoneuron firing during each fictive step cycle were characterized by increased frequency and number of spikes after MEC, although the burst duration was unaltered for similar step cycle lengths. A greater number and frequency of spikes per burst was also observed in Ia inhibitory interneurons (IaINs), which remained rhythmically active after MEC administration. It is concluded that Renshaw cells are not an integral part of the spinal central pattern generator for locomotion, nor do they control the timing of the motoneuron or IaIN bursts of firing during fictive locomotion. The data are consistent with a role for RCs in limiting the firing rates of motoneurons and IaINs during each burst.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00236206
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  • 3
    Electronic Resource
    Electronic Resource
    Reversible cooling of the brainstem reveals areas required for mesencephalic locomotor region evoked treadmill locomotion (1984)
    Springer
    Experimental brain research 56 (1984), S. 257-262 
    Details
    ISSN: 1432-1106
    Keywords: Locomotion ; Mesencephalic locomotor region ; Pontomedullary strip ; Reversible cooling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The evidence suggests that the mesencephalic locomotor region (MLR) may not be a unitary region since anatomical and functional variations in the descending projections are clearly indicated. Reversible cooling of midline reticular structures can effectively block locomotion evoked by stimulation of lateral MLR (L3.5–4) sites while not significantly affecting the locomotion evoked from more medial MLR (L2–2.5) sites. In contrast, locomotion evoked by stimulation of the medial MLR sites is blocked by cooling of the ipsilateral lateral brainstem region which corresponds to the pontomedullary strip (PLS). Ipsilateral PLS cooling was not effective for blocking lateral MLR evoked locomotion, and contralateral PLS cooling was not effective for blocking either medial or lateral MLR evoked stepping. The evidence indicates that the lateral MLR relays through medial reticular nuclei while the medial MLR sites relay largely through the lateral brainstem structures often referred to as the PLS.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00236281
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  • 4
    Electronic Resource
    Electronic Resource
    Spinal distribution of extracellular field potentials generated by electrical stimulation of pudendal and perineal afferents in the cat (1992)
    Springer
    Experimental brain research 89 (1992), S. 517-520 
    Details
    ISSN: 1432-1106
    Keywords: Sacral reflexes ; Micturition ; Interneurons
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Electrical stimulation of sensory pudendal and superficial perineal nerves evokes focal synaptic potentials produced by activation of spinal neurons in the lumbosacral gray matter in chloralose anesthetized or decerebrate cats. The field potentials evoked by sensory pudendal nerve stimulation were located in medial parts of laminae V and VI, and lamina X in the S1 to S3 spinal segments. The superficial perineal cutaneous field potentials partially overlapped with those produced by the pudendal nerve, but in general were localized more laterally in laminae V and VI. The central latencies of the earliest portion of the field potentials evoked by either sensory pudendal or superficial perineal nerves were less than 0.9 ms suggesting that monosynaptic activation of neurons contributed to the potentials.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00229876
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  • 5
    Electronic Resource
    Electronic Resource
    An intracellular study of perineal and hindlimb afferent inputs onto sphincter motoneurons in the decerebrate cat (1992)
    Springer
    Experimental brain research 89 (1992), S. 511-516 
    Details
    ISSN: 1432-1106
    Keywords: Micturition ; Defecation ; Sphincter ; Cutaneous ; Spinal cord reflexes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00229875
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  • 6
    Electronic Resource
    Electronic Resource
    On the regulation of repetitive firing in lumbar motoneurones during fictive locomotion in the cat (1992)
    Springer
    Experimental brain research 90 (1992), S. 441-455 
    Details
    ISSN: 1432-1106
    Keywords: Afterhyperpolarisation ; Motoneurone ; Fictive locomotion ; Repetitive firing ; Cat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Repetitive firing of motoneurones was examined in decerebrate, unanaesthetised, paralysed cats in which fictive locomotion was induced by stimulation of the mesencephalic locomotor region. Repetitive firing produced by sustained intracellular current injection was compared with repetitive firing observed during fictive locomotion in 17 motoneurones. During similar interspike intervals, the afterhyperpolarisations (AHPs) during fictive locomotion were decreased in amplitude compared to the AHPs following action potentials produced by sustained depolarising current injections. Action potentials were evoked in 10 motoneurones by the injection of short duration pulses of depolarising current throughout the step cycles. When compared to the AHPs evoked at rest, the AHPs during fictive locomotion were reduced in amplitude at similar membrane potentials. The post-spike trajectories were also compared in different phases of the step cycle. The AHPs following these spikes were reduced in amplitude particularly in the depolarised phases of the step cycles. The frequency-current (f-I) relations of 7 motoneurones were examined in the presence and absence of fictive locomotion. Primary ranges of firing were observed in all cells in the absence of fictive locomotion. In most cells (6/7), however, there was no relation between the amount of current injected and the frequency of repetitive firing during fictive locomotion. In one cell, there was a large increase in the slope of the f-I relation. It is suggested that this increase in slope resulted from a reduction in the AHP conductance; furthermore, the usual elimination of the relation is consistent with the suggestions that the repetitive firing in motoneurones during fictive locomotion is not produced by somatic depolarisation alone, and that motoneurones do not behave as simple input-output devices during this behaviour. The correlation of firing level with increasing firing frequency which has previously been demonstrated during repetitive firing produced by afferent stimulation or by somatic current injection is not present during fictive locomotion. This lends further support to the suggestion that motoneurone repetitive firing during fictive locomotion is not produced or regulated by somatic depolarisation. It is suggested that although motoneurones possess the intrinsic ability to fire repetitively in response to somatic depolarisation, the nervous system need not rely on this ability in order to produce repetitive firing during motor acts. This capability to modify or bypass specific motoneuronal properties may lend the nervous system a high degree of control over its motor output.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00230927
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  • 7
    Electronic Resource
    Electronic Resource
    Effects of electrical stimulation of the thoracic spinal cord on bladder and external urethral sphincter activity in the decerebrate cat (1991)
    Springer
    Experimental brain research 84 (1991), S. 635-642 
    Details
    ISSN: 1432-1106
    Keywords: Micturition ; Spinal cord lesions ; Thoracic spinal cord ; Pudendal
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00230976
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