[Cellular regulation of the lower urinary tract as a cause of the bladder overactivity and reduced efficiency of pharmacotherapy]

Overactive bladder (OAB) is a polyetiological nosology. Its symptoms are often characterized not only with detrusor hyperactivity, but also with the increased sensitivity of afferent fibers, which is clinically manifested as urgency. In addition, the disorders at the level of receptors expression and the synthesis of mediators lead to the development of bladder pain syndrome (BPS), which also significantly reduces the quality of life of patients. In recent years, the experimental animal studies achieved significant progress in understanding of the pathogenesis of lower urinary tract dysfunction. In particular, the broad understanding of the sensor properties of urothelium was obtained, which significantly increased the popularity of the urothelial theory of the development of idiopathic detrusor hyperactivity, as well as hypersensitivity and bladder pain. According to this theory, the pathological release of biologically active substance in the transitional epithelium in response to an extension of the bladder wall leads to clinical manifestations of the described conditions. In addition, due to the studies of the properties of receptors, ion channels, and mediators, the suggestion about the reduced efficiency of muscarinic receptor antagonists have been made in a large number of patients. Besides the acetylcholine control of the lower urinary tract, more and more attention is paid to other significant mechanisms of pathological conditions. The purpose of this part of the lecture is to systematize the available materials of basic research on the functioning of the lower urinary tract at the cellular level, as well as the mechanisms of action and questions of the effectiveness of pharmacological therapy for urinary disorders.

[Characteristics of the neural regulation of the lower urinary tract as a cause of the development of an overactive bladder: current state of the problem]

An overactive bladder (OAB) is a constellation of lower urinary tract symptoms, including urgency, increased frequency of urination during the day and/or night (nocturia), and, in some cases, urge incontinence. This syndrome can be caused by different conditions, and currently no universal pathogenetic treatment has been developed. In addition, there are virtually no Russian-language publications providing information on the neurophysiology and neuroanatomy of the lower urinary tract. At the same time, the importance of this topic can hardly be overestimated. Often, a patient with a neurogenic dysfunction of the lower urinary tract has different comorbidities, which requires to deeply understand the mechanisms of development of certain symptoms. Considering an absence of clear data about the peripheral bladder innervation, role of the structures of the central nervous system and importance of neurotransmitters, it is rather difficult to provide high-quality specialized care. However, in recent years, a lot of new facts and theories have been described in basic researches. This lecture is dedicated to the current data on the pathogenesis of OAB. The purpose of the lecture is to summarize the results of fundamental and clinical studies on the pathogenesis of OAB.

[SIGNALING PATHWAYS REGULATING PROTEIN SYNTHESIS IN RAT SOLEUS MUSCLE DURING EARLY STAGES OF HINDLIMB UNLOADING]

The impact of mechanical unloading (hindlimb suspension for 1-, 3- and 7 days) on the protein synthesis intensity and as well as intracellular signaling pathways controlling mRNA translation was investigated. The content of the key signaling molecules of the various anabolic signaling pathways was determined by Western-blotting. The rate of protein synthesis was assessed using in vivo SUnSET technique. Hindlimb suspension (HS) within 24 hours resulted in a significant (p < 0.05) decrease in p-4E-BP 1 content and increase in p-p70s6k content in soleus muscle. Follo- wing three days of HS the content of p-AKT and p-90RSK1 was decreased (p <0.05). After 7 days of HS phosphorylation level of AKT and GSK-3beta was significantly reduced (p < 0.05) compared to the control group. We also observed a significant decrease in the amount of 28S rRNA in soleus following 3 and 7 days of HS. The rate of protein synthesis after 3 and 7 days of HS was decreased (p < 0.05) in comparison with the basal level. Our data suggest that the decrease in the protein synthesis rate in rat soleus during early stages of simulated microgravity could be associated with the impaired ribosome biogenesis as well as reduced activity of the mTORC1-independent signaling pathways.

[Mathematical model of the hindlimbs control during cat locomotion with balance]

The musculoskeletal model of cat's hind limbs, capable to step while maintaining balance, was developed using the MatLab. The skeletal part of the model (spine, pelvis, hips, shanks, foots) was created at SimMechanics. The joint in the spine attachment to the support and hip joint have three degrees of freedom. Knee and ankle joints have one degree of freedom. The pelvis is rigidly connected to the spine. The control of the skeleton's segments is done by six groups of muscles (flexors and extensors of hips, knees and ankles), modeled using the package VirtualMuscle. The generalized lateral force exerted on the spine was introduced to compensate insecure lateral deviations. Experimental verification of the model realness have shown that its locomotor characteristics (e. g., muscles activation patterns, oscillation period of pelvis, correlation between step length and maximal lateral shift of pelvis) do not significantly differ from the locomotion of decerebrate cats. The simulation confirms the key role of lateral force evolved by paravertebral and abductor-adductor muscles in the control of lateral stability during locomotion.

[Non-invasive transcutaneous spinal cord stimulation facilitates locomotor activity in decerebrated and spinal cats]

It is known that spinal neuronal networks activated by epidural electrical stimulation (EES) can produce the stepping EMG pattern and control the locomotor behavior. At present study we showed that non-invasive transcutaneous electrical spinal cord stimulation (tESCS) applied to the lumbar-sacral enlargement can facilitate the locomotor activity in decerebrated and spinal animals. The comparison of the motor responses evoked by EES vs tESCS showed that both methods produce the locomotor patterns with close properties and similar reflex mechanisms. The data obtained suggest that tESCS is an efficient approach for investigation of the locomotor control in acute and chronic experiments as well as facilitates of the locomotor abilities after spinal cord injury. Taking to account the non-invasivity and easement of tESCS, this approach could be further implemented in clinical practice for rehabilitation of the patient with spinal cord injury.

[Neuronal control of posture and locomotion in decerebrated and spinalized animals]

We have found that the brainstem-spinal cord circuitry of decerebrated cats actively maintain the equilibrium during standing, walking and imposed mechanical perturbations similar to that observed in intact animals. The corrective hindlimb motor responses during standing included redistribution of the extensor activity ipsilateral and contralateral to perturbation. The postural corrections in walking cats were due to considerable modification of EMG pattern in the limbs as well as changing of the swing-stance phases of the step cycle and ground reaction forces depending of perturbation side. Thus the basic mechanisms for balance control of decerebrated animals in these two forms of motor behavior are different. Balance-related adjustments relied entirely on the integration of somatosensory information arising from the moving hindquarters because of the suppression of vestibular, visual, and head-neck-trunk sensory input. We propose that the somatosensory input from the hindquarters in concert with the lumbosacral spinal circuitry can control the dynamics of the hindquarters sufficient to sustain balance. We found that, after isolation from the brainstem or forebrain, lumbosacral circuits receiving tonic epidural electrical stimulation can effectively control equilibrium during standing and stepping. Detailed analyses of the relationships among muscle activity, trunk kinematics, and limb kinetics indicate that spinal motor systems utilize a combination of feedback and feedforward strategies to maintain dynamic equilibrium during walking. The unexpected ability of spinal circuitries to exert efficient postural control in the presence of epidural electrical stimulation in decerebrated and spinal cats have significant implications for the potential of humans with a severe spinal cord injury to regain a significant level of functional standing and walking capacities.

[Analysis of locomotor activity in decerebrated cats during electromagnetic and epidural electrical spinal cord stimulation]

It was shown that the epidural and the electromagnetic tonic stimulation with frequency 5 Hz applied to the lumbal as well as to the cervical region of the spinal cord enabled stepping on a moving treadmill belt in decerebrated cats. It was found that there were differences in initiation of the stepping movements during epidural and electromagnetic stimulation depending on the region of spinal cord stimulation. Stimulation at frequency of 0.3 Hz induced single reflex responses in the anterior and posterior limbs. On the basis of analysis of the response structure it was concluded that the locomotor ability during epidural and electromagnetic stimulation depended on the degree of polysynaptic pathways activation. The hypothesis about stepping pattern generator activation through the dorsal roots during epidural stimulation and more direct activation of neuronal locomotor networks in the case of electromagnetic spinal cord stimulation is discussed.

Facilitation of postural limb reflexes with epidural stimulation in spinal rabbits

It is known that after spinalization animals lose their ability to maintain lateral stability when standing or walking. A likely reason for this is a reduction of the postural limb reflexes (PLRs) driven by stretch and load receptors of the limbs. The aim of this study was to clarify whether spinal networks contribute to the generation of PLRs. For this purpose, first, PLRs were recorded in decerebrated rabbits before and after spinalization at T12. Second, the effects of epidural electrical stimulation (EES) at L7 on the limb reflexes were studied after spinalization. To evoke PLRs, the vertebrate column of the rabbit was fixed, whereas the hindlimbs were positioned on the platform. Periodic lateral tilts of the platform caused antiphase flexion-extension limbs movements, similar to those observed in intact animals keeping balance on the tilting platform. Before spinalization, these movements evoked PLRs: augmentation of extensor EMGs and increase of contact force during limb flexion, suggesting their stabilizing postural effects. Spinalization resulted in almost complete disappearance of PLRs. After EES, however, the PLRs reappeared and persisted for up to several minutes, although their values were reduced. The post-EES effects could be magnified by intrathecal application of quipazine (5-HT agonist) at L4-L6. Results of this study suggest that the spinal cord contains the neuronal networks underlying PLRs; they can contribute to the maintenance of lateral stability in intact subjects. In acute spinal animals, these networks can be activated by EES, suggesting that they are normally activated by a tonic supraspinal drive.

[Mechanisms of stepping rhythm formation during epidural spinal cord stimulation in decerebrated and spinal cord transected cats]

The mechanisms of stepping pattern formation during epidural spinal cord stimulation in decerebrated and chronically spinal cord transected cats have been investigated. The features of the stepping performance in hindlimb muscles depending on the parameters of epidural stimulation and afferent input were determined. It was shown that, at nonoptimal parameters of stimulation, stepping movements are not induced. In response to the stimulation, reflectory muscle responses are evoked only. Epidural stimulation with optimal parameters induces coordinated stepping movements in hindlimbs with normal rhythm (0.8-1 Hz), which is accompanied by the electromyographic bursting activity of the corresponding muscles. In decerebrated cats, the formation of electromyographic bursts occurs due to the modulation of early responses and the late polysynaptic activity. In chronically spinal cord transected cats, this process is provided mainly by the amplitude modulation of early responses. The formation of the stepping pattern in decerebrated cats with the participation of spinal interneurons responsible for the polysynaptic activity allows one to perform its correction on the basis of the processing of afferent signals. The activation of this system in chronically spinal cord transected cats can be realized by afferent stimulation alone.

[Locomotion induced by epidural stimulation in decerebrate cat after spinal cord injury]

The effect of partial and complete spinal cord injury (Th7-Th8) on locomotor activity evoked by epidural electrical stimulation (L5 segment, stimulation frequency 5 Hz, current strength 80-100 microA) in decerebrate cats has been investigated. It was established that the cutting of dorsal columns did not influence substantially the locomotion. The destruction of the ventral spinal quadrant resulted in the deterioration and instability of the locomotor rhythm. The injury of lateral or medial descending motor systems led to a redistribution of the tone in antagonist muscles. It was found that locomotion can be evoked by epidural stimulation within 20 h after the complete transaction of the spinal cord. The restoration of polysynaptic components in EMG responses correlated with the restoration of the stepping function. The data obtained confirm that the initiation of locomotion under epidural stimulation is caused by direct action on intraspinal systems responsible for locomotion regulation. In the case of intact or partially injured spinal cord, this effect is under the influence of supraspinal motor systems correcting and stabilizing the evoked locomotor pattern.

Effect of intrathecal administration of serotoninergic and noradrenergic drugs on postural performance in rabbits with spinal cord lesions

Our previous studies have shown that extensive spinal lesions at T12 in the rabbit [ventral hemisection (VHS) or 3/4-section that spares one ventral quadrant (VQ)] severely damaged the postural system. When tested on the platform periodically tilted in the frontal plane, VHS and VQ animals typically were not able to perform postural corrective movements by their hindlimbs, although EMG responses (correctly or incorrectly phased) could be observed. We attempted to restore postural control in VHS and VQ rabbits by applying serotoninergic and noradrenergic drugs to the spinal cord below the lesion through the intrathecal cannula. It was found that serotonin and quipazine (5-HT1,2,3 agonist) did not re-establish postural corrective movements. However, when applied during a 10-day period after lesion, these drugs produced a twofold increase of the proportion of correct EMG responses to tilts. It was also found that methoxamine (alpha1 noradrenergic agonist), as well as the mixture of methoxamine and quipazine, did not re-establish postural corrective movements and did not increase the proportion of correct EMG responses. Serotonin (at later stages) and methoxamine induced periodical bursting in EMGs, suggesting activation of spinal rhythm-generating networks. Appearance of bursting seems to perturb normal operation of postural mechanisms, as suggested by methoxamine-induced abolishment of postural effects of quipazine. When applied in an intact animal, none of the tested drugs affected the value of postural corrections or evoked periodical bursting. We conclude that activation of the serotoninergic system (but not the noradrenergic one) causes selective enhancement of spinal postural reflexes during the earlier postlesion period.

Postural performance in decerebrated rabbit

It is known that animals decerebrated at the premammillary level are capable of standing and walking without losing balance, in contrast to postmammillary ones which do not exhibit such behavior. The main goals of the present study were, first, to characterize the postural performance in premammillary rabbits, and, second, to activate the postural system in postmammillary ones by brainstem stimulation. For evaluation of postural capacity of decerebrated rabbits, motor and EMG responses to lateral tilts of the supporting platform and to lateral pushes were recorded before and after decerebration. In addition, the righting behavior (i.e., standing up from the lying position) was video recorded. We found that, in premammillary rabbits, responses to lateral tilts and pushes were similar to those observed in intact ones, but the magnitude of responses was reduced. During righting, premammillary rabbits assumed the normal position slower than intact ones. To activate the postural system in postmammillary rabbits, we stimulated electrically two brainstem structures, the mesencephalic locomotor region (MLR) and the ventral tegmental field (VTF). The MLR stimulation (prior to elicitation of locomotion) and the VTF stimulation caused an increase of the tone of hindlimb extensors, and enhanced their responses to lateral tilts and to pushes. These results indicate that the basic mechanisms for maintenance of body posture and equilibrium during standing are present in decerebrated animals. They are active in the premammillary rabbits but need to be activated in the postmammillary ones.

Significance of peripheral feedback in the generation of stepping movements during epidural stimulation of the spinal cord

Acute experiments on decerebrate and spinal cats were performed to study the role of the peripheral afferent input from hindlimb receptors in forming the locomotor pattern during epidural stimulation of the spinal cord. Evoked electromyographic activity in the muscles of the hindlimbs was analyzed, along with the kinematic parameters of stepping movements. Epidural stimulation (20-100 microA, 5 Hz) of segments L4-5 of the spinal cord was found to elicit well coordinated walking in the hindlimbs on a moving treadmill band. When the support conditions were changed (non-moving treadmill, unsupported position), epidural stimulation initiated walking with an unstable rhythm. This was associated with a change in the overall nature of the locomotor pattern and the internal structure of the stepping cycle. Alteration of the direction of movement of the treadmill band led to the appearance of backward walking. An increase in the speed of movement of the treadmill band increased the stepping frequency, mainly due to decreases in the extensor phase. Epidural stimulation applied 2-4 h after complete transection of the spinal cord at the T8-T9 level could elicit stepping movements, but only when the treadmill was moving. The role of peripheral feedback in generating the locomotor pattern in conditions of complete disconnection from supraspinal control increased significantly. These data show that peripheral feedback during epidural stimulation of the spinal cord can define the properties of the motor output.

[Significance of peripheral feedback in stepping movement generation under epideral spinal cord stimulation]

In acute experiments on decerebrated and spinalized cats, the role of peripheral afferent input from hindlimbs in stepping patterns formation under epidural spinal cord stimulation (ESCS), was investigated. The hindlimb muscles' electromyographic activity and kinematic parameters of evoked stepping were analyzed. It has been shown that epidural stimulation (20-100 microA, 5 Hz) of L4-L5 spine segments induced coordinated stepping on the treadmill belt. In conditions of weight-bearing support (stopped treadmill, hindlimbs lifted above the treadmill), the stepping rhythmic was unstable, stepping cycle period and its internal structure having changed as well. With increased speed of locomotion the stepping frequency increased due to the duration of the support phase decreasing. Forward stepping could be reversed to backward stepping by changing the direction of the treadmill belt movement. In 2-4 hours after complete spinal transection (T8-T9), the epidural stimulation elicited stepping movements on a moving treadmill only. It was found that the influence of peripheral feedback on initiation of the stepping after spinalization increased. Peripheral feedback seems to play a major role in determining the fundamental features of motor output during the ESCS.

Formation of locomotor patterns in decerebrate cats in conditions of epidural stimulation of the spinal cord

Acute experiments on decerebrate cats were performed to study the mechanism of formation of the locomotor pattern in conditions of epidural stimulation of the spinal cord. These studies showed that only segments L3-L5 contributed to generating the stepping pattern in the hindlimbs. At the optimum frequency (5-10 Hz) of stimulation of these segments, formation of electromyographic burst activity in the flexor muscles was mainly due to polysynaptic reflex responses with latencies of 80-110 msec. In the extensor muscles, this process involved the interaction of a monosynaptic reflex and polysynaptic activity. In epidural stimulation, the stepping pattern was specified by spinal structures, while peripheral feedback had modulatory influences.

[Features of stepping pattern formation in decerebrated cats under epidural spinal cord stimulation]

The mechanisms of stepping pattern formation initiated by epidural spinal cord stimulation in decerebrated cats, were investigated. It is shown that the ability to produce the stepping pattern involve the L3-L5 segments. In flexor muscle, the formation of stepping pattern under optimal stimulation frequency (5-10 Hz) of these segments is provided by polysynaptic activity with the latency 80-110 ms. In extensor muscle, this process is realized through interaction of monosynaptic reflex and polysynaptic activity. The stepping pattern under epidural stimulation is determined by spinal structures with modulation influence of the peripheral feedback.