Spatiotemporal mapping of spontaneous smooth muscle motility in capacious organs: the ex vivo urinary bladder and in vivo gravid uterus of the rabbit: a thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Massey University, Palmerston North, New Zealand
| dc.confidential | Embargo : No | |
| dc.contributor.advisor | Lentle, Roger | |
| dc.contributor.author | Hulls, Corrin | |
| dc.date.accessioned | 2023-11-29T23:06:46Z | |
| dc.date.available | 2023-11-29T23:06:46Z | |
| dc.date.issued | 2023-08-20 | |
| dc.description.abstract | The temporal and spatial dynamics of propagating myogenic contractions in the wall of the resting ex vivo urinary bladder and in vivo gravid uterus of the rabbit were characterised by spatiotemporal maps of area strain rate, of linear strain rate and contractile patch analysis, and related to cyclic variation in intravesical pressure (pves) in the bladder, and electrophysiological recordings in the gravid uterus. In the urinary bladder, patches of propagating contractions (PPCs) enlarged and involuted with a frequency in near synchrony with peaks in intravesical pressure. Maximum area percentage of the anterior surface of the bladder undergoing contraction and the sizes of individual PPCs also coincided with the peak in pves. Moreover, pves varied cyclically with total area of contraction and with the indices of the size and aggregation of PPCs, indicating that PPCs grew and involuted by a combination of peripheral enlargement or shrinkage and by coalescence or fission with other PPCs, their areas being maximal at or around the peak in pves. Bladder PPCs originated and propagated within temporary patch domains (TPDs) and comprised groups of near synchronous cyclic individual contractions (PICs). The TPDs were located principally along the vertical axis of the anterior surface of the bladder, either to the left or the right of midline and changed in location from one side to side and from side to tip or base. The sites of origin of PICs within PPCs were inconsistent, consecutive contractions often propagating in opposite directions along linear maps of strain rate. Similar patterns of movement of PPCs within TPDs of the same form occurred in areas of the anterior bladder wall that had been stripped of mucosa. The synchronisation and extended propagation of PICs within PPCs and the concurrent variation in pves of the bladder were sometimes lost or diminished, uncoordinated PICs then occurred, propagated shorter distances, and had little effect on pves. There was no evidence that any influence of bladder shape on stress influenced the principal direction of propagation of either PCCs or PICs or the disposition of TPDs. The disposition and dynamics of PPCs and their component individual myogenic contractions in the wall of the resting ex vivo tetrodotoxinized urinary bladder of the rabbit were characterised by spatiotemporal maps and related to cyclic variation in pves before and after the administration of carbachol, isoprenaline, carbenoxolone, and the RhoA-inhibitor Y-27632. The results confirm that the bladder wall can exhibit two contractile states that are of similar frequencies to those of the two types of electrophysiological discharge described by previous workers. In the first of these, large low frequency cyclic PPCs predominate. In the second, small irregular, higher frequency PICs predominate. Comparison of the effects of the drugs on the timing and disposition of contraction suggested indicated that the local spatial spread of contractions in PPCs was governed largely by myocytes, whilst the propagation, frequency, and duration of PPCs was likely governed via gap junctions between interstitial cells of cajal- intermuscular (ICC-IM) and myocytes. Spontaneous and oxytocin-induced contractile activity was quantified in the bicornuate uteri of pregnant rabbits maintained in situ, using data from electrophysiological recordings and spatiotemporal maps, and compared statistically. Spontaneous contractions occurred over a range of frequencies in gravid animals at 18-21 and at 28 days of gestation and propagated both radially and longitudinally over the uterine wall overlying each foetus. Patches of contractions were randomly distributed over the entire surface of the cornua and were pleomorphic in shape. No spatial coordination was evident between longitudinal and circular muscle layers nor temporal coordination that could indicate the activity of a localised pacemaker. The density and duration of contractions decreased, and their frequency increased with the length of gestation in the non-labouring uterus. Increasing intravenous doses of oxytocin had no effect on the mean frequencies, or the mean durations of contractions in rabbits of 18-21 days gestation but caused frequencies to decrease and durations to increase in rabbits of 28 days gestation, from greater spatial and temporal clustering of individual contractions. This was accompanied by an increase in the distance of propagation, the mean size of the patches of contraction, the area of the largest patch of contraction and the overall density of patches. Together these results suggest that progressive smooth muscle hypertrophy and displacement with increasing gestation is accompanied by a decrease in smooth muscle connectivity causing an increase in wall compliance and that oxytocin restores connectivity and decreases compliance, promoting volumetric expulsion rather than direct propulsion of the foetus by peristalsis. The latter effects were reversed by the β2 adrenergic receptor agonist salbutamol thus reducing area of contraction, duration, and distance of propagation. The characteristics of smooth muscle contraction that are associated with the maintenance of tone during accommodation appear to be to be similar in the capacious organs discussed. Hence, it appears there is patchy rather than uniform local revision of the state of tonal contraction over the surfaces of the various capacious organs during accommodation that can undergo neural modulation. There appears to be less similarity in regard to the mechanisms that secure the voiding contractions in these capacious structures. Whilst the actuation of the necessary shorter term increase in tone may be ultimately dependent upon a mechanosensitive myogenic reflex, the relative contributions of autonomic, hormonal, mechanical and voluntary reflexes that reset the threshold of this reflex and aid in the relatively rapid expulsion of the contents, appear to vary between organs. | |
| dc.identifier.uri | https://mro.massey.ac.nz/handle/10179/69224 | |
| dc.publisher | Massey University | en |
| dc.rights | The Author | en |
| dc.subject | Bladder | en |
| dc.subject | Uterus | en |
| dc.subject | Muscles | en |
| dc.subject | Motility | en |
| dc.subject | Rabbits | en |
| dc.subject | Physiology | en |
| dc.subject | spatiotemporal, motility, tone, compliance | |
| dc.subject.anzsrc | 310908 Animal physiology - biophysics | en |
| dc.subject.anzsrc | 310911 Animal structure and function | en |
| dc.title | Spatiotemporal mapping of spontaneous smooth muscle motility in capacious organs: the ex vivo urinary bladder and in vivo gravid uterus of the rabbit: a thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Massey University, Palmerston North, New Zealand | |
| thesis.degree.discipline | Anatomy, Physiology and Biomechanics | |
| thesis.degree.name | Doctor of Philosophy (Ph.D.) | |
| thesis.description.doctoral-citation-abridged | Mr Hulls investigated the spontaneous smooth muscle motility in capacious organs of the ex vivo urinary bladder and in vivo gravid uterus of the rabbit. His findings showed that modulation of tone was similar in the bladder and gravid uterus with patchy rather than uniform local revision of the state of tonal contraction that was further influenced by neural modulation. | |
| thesis.description.doctoral-citation-long | Both the bladder and gravid uterus are volume accommodating organs. Muscle changes in wall compliance of a capacious organ allow accommodation of incoming material without a large change in luminal pressure. The process of volume compliance within structures of the human body is not completely understood, however, it is controlled by a combination of the inherent elasticity of the tissue of the wall (passive tone) coupled with a change in the frequency of tonic contractions (active tone). The technique of spatiotemporal mapping was used to the measure the characteristics of smooth muscle contraction that are associated with the maintenance of tone during accommodation. It was found that modulation of tone was similar in the bladder and gravid uterus. Moreover, there was patchy rather than uniform local revision of the state of tonal contraction over the surfaces of the various capacious organs during accommodation that were influenced by neural modulation. In contrast, there appeared to be less similarity in regard to the mechanisms that secure the voiding contractions in these capacious structures. | |
| thesis.description.name-pronounciation | Cor-rin |
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