Behavioral analysis of the postnatal development of micturition in kittens

Model-based analysis of the acute effects of transcutaneous magnetic spinal cord stimulation on micturition after spinal cord injury in humans

AIM

After spinal cord injuries (SCIs), patients may develop either detrusor-sphincter dyssynergia (DSD) or urinary incontinence, depending on the level of the spinal injury. DSD and incontinence reflect the loss of coordinated neural control among the detrusor muscle, which increases bladder pressure to facilitate urination, and urethral sphincters and pelvic floor muscles, which control the bladder outlet to restrict or permit bladder emptying. Transcutaneous magnetic stimulation (TMS) applied to the spinal cord after SCI reduced DSD and incontinence. We defined, within a mathematical model, the minimum neuronal elements necessary to replicate neurogenic dysfunction of the bladder after a SCI and incorporated into this model the minimum additional neurophysiological features sufficient to replicate the improvements in bladder function associated with lumbar TMS of the spine in patients with SCI.

METHODS

We created a computational model of the neural circuit of micturition based on Hodgkin-Huxley equations that replicated normal bladder function. We added interneurons and increased network complexity to reproduce dysfunctional micturition after SCI, and we increased the density and complexity of interactions of both inhibitory and excitatory lumbar spinal interneurons responsive to TMS to provide a more diverse set of spinal responses to intrinsic and extrinsic activation of spinal interneurons that remains after SCI.

RESULTS

The model reproduced the re-emergence of a spinal voiding reflex after SCI. When we investigated the effect of monophasic and biphasic TMS at two frequencies applied at or below T10, the model replicated the improved coordination between detrusor and external urethral sphincter activity that has been observed clinically: low-frequency TMS (1 Hz) within the model normalized control of voiding after SCI, whereas high-frequency TMS (30 Hz) enhanced urine storage.

CONCLUSION

Neuroplasticity and increased complexity of interactions among lumbar interneurons, beyond what is necessary to simulate normal bladder function, must be present in order to replicate the effects of SCI on control of micturition, and both neuronal and network modifications of lumbar interneurons are essential to understand the mechanisms whereby TMS reduced bladder dysfunction after SCI.

Postnatal growth of the lumbosacral spinal segments in cat: Their lengths and positions in relation to vertebrae

Cat is a prominent model for investigating neural networks of the lumbosacral spinal cord that control locomotor and visceral activity. We previously proposed an integral function, establishing the topographical relationship between the spinal cord segments and vertebrae in adult animals. Here, we investigated the dynamic of this topographical relationship through early and middle periods of development in kittens. We calculated the length of each vertebra relative to the total length of the region from 13th thoracic (T) to the 7th lumbar (L) vertebrae (V) as well as the length of each segment relative to the total region from T13 to the three-dimensional sacral (S) segment. As in our previous work, the length and position of VL2 were used to establish relationships between the characteristics of the segments and vertebrae. Cubic regression reliably approximates the lengths of segments relative to VL2 length. As the cat aged, the relative length of VT13 and VL1 decreased while the relative length of VL5 increased. The relative length of the T13 and L3 segments increased while the relative length of the S1-S2 segments decreased. The T13-L2 segments are descended monotonically relative to the VL1-VL2 border. The L3-S1 segments are also descended, though with more complex dynamics. The positions of the S2-S3 segments remained unchanged. To conclude, different spinal segments displayed different developmental dynamics. The revealed relationship between vertebrae and lumbosacral spinal segments may be helpful for clearly defining stimulation regions to invoke particular functions, both in experimental studies on the spinal cord and clinical treatment.

A review of the neural control of micturition in dogs and cats: neuroanatomy, neurophysiology and neuroplasticity

This article discusses the current knowledge on the role of the neurological structures, especially the cerebellum and the hypothalamus, and compares the information with human medicine. Micturition is a complex voluntary and involuntarily mechanism. Its physiological completion strictly depends on the hierarchical organisation of the central nervous system pathways in the peripheral nervous system. Although the role of the peripheral nervous system and subcortical areas, such as brainstem centres, are well established in veterinary medicine, the role of the cerebellum and hypothalamus have been poorly investigated and understood. Lower urinary tract dysfunction is often associated with neurological diseases that cause neurogenic bladder (NB). The neuroplasticity of the nervous system in the developmental changes of the mechanism of micturition during the prenatal and postnatal periods is also analysed.

Daily maternal separations during stress hyporesponsive period decrease the thresholds of panic-like behaviors to electrical stimulation of the dorsal periaqueductal gray of the adult rat

The present study examined whether early life maternal separation (MS), a model of childhood separation anxiety, predisposes to panic at adulthood. For this purpose, male pups were submitted to 3-h daily maternal separations along postnatal (PN) days of either the 'stress hyporesponsive period' (SHRP) from PN4 to PN14 (MS11) or throughout lactation from PN2 to PN21 (MS20). Pups were further reunited to conscious (CM) or anesthetized (AM) mothers to assess the effect of mother-pup interaction upon reunion. Controls were subjected to brief handling (15 s) once a day throughout lactation (BH20). As adults (PN60), rats were tested for the thresholds to evoke panic-like behaviors upon electrical stimulation of dorsal periaqueductal gray matter and exposed to an elevated plus-maze, an open-field, a forced swim and a sucrose preference test. A factor analysis was also performed to gain insight into the meaning of behavioral tests. MS11-CM rather than MS20-CM rats showed enhanced panic responses and reductions in both swimming and sucrose preference. Panic facilitations were less intense in mother-neglected rats. Although MS did not affect anxiety, MS11-AM showed robust reductions of defecation in an open-field. Factor analysis singled out anxiety, hedonia, exploration, coping and gut activity. Although sucrose preference and coping loaded on separate factors, appetite (adult weight) correlated with active coping in both forced swim and open-field (central area exploration). Concluding, whereas 3h-daily maternal separations during SHRP increased rat's susceptibility to experimental panic attacks, separations throughout lactation had no effects on panic and enhanced active coping.

Genitourinary and gastrointestinal co-morbidities in children: The role of neural circuits in regulation of visceral function

OBJECTIVE

Pediatric lower urinary tract dysfunction (LUTD) is a common problem in childhood. Lower urinary tract symptoms in children include overactive bladder, voiding postponement, stress incontinence, giggle incontinence, and dysfunctional voiding. Gastrointestinal co-morbidities, including constipation or fecal incontinence, are commonly associated with lower urinary tract (LUT) symptoms in children, often reaching 22-34%. This review summarized the potential mechanisms underlying functional lower urinary and gastrointestinal co-morbidities in children. It also covered the current understanding of clinical pathophysiology in the pediatric population, anatomy and embryological development of the pelvic organs, role of developing neural circuits in regulation of functional co-morbidities, and relevant translational animal models.

MATERIALS AND METHODS

This was a non-systematic review of the published literature, which summarized the available clinical and translational studies on functional urologic and gastrointestinal co-morbidities in children, as well as neural mechanisms underlying pelvic organ 'cross-talk' and 'cross-sensitization'.

RESULTS

Co-morbidity of pediatric lower urinary and gastrointestinal dysfunctions could be explained by multiple factors, including a shared developmental origin, close anatomical proximity, and pelvic organ 'cross-talk'. Daily physiological activity and viscero-visceral reflexes between the lower gastrointestinal and urinary tracts are controlled by both autonomic and central nervous systems, suggesting the dominant modulatory role of the neural pathways. Recent studies have provided evidence that altered sensation in the bladder and dysfunctional voiding can be triggered by pathological changes in neighboring pelvic organs due to a phenomenon known as pelvic organ 'cross-sensitization'. Cross-sensitization between pelvic organs is thought to be mainly coordinated by convergent neurons that receive dual afferent inputs from discrete pelvic organs. Investigation of functional changes in nerve fibers and neurons sets certain limits in conducting appropriate research in humans, making the use of animal models necessary to uncover the underlying mechanisms and for the development of novel therapeutic approaches for long-term symptomatic treatment of LUTD in the pediatric population.

CONCLUSION

Pediatric LUTD is often complicated by gastrointestinal co-morbidities; however, the mechanisms linking bladder and bowel dysfunctions are not well understood. Clinical studies have suggested that therapeutic modulation of one system may improve the other system's function. To better manage children with LUTD, the interplay between the two systems, and how co-morbid GI and voiding dysfunctions can be more specifically targeted in pediatric clinics need to be understood.

Neural control of the lower urinary tract

This article summarizes anatomical, neurophysiological, pharmacological, and brain imaging studies in humans and animals that have provided insights into the neural circuitry and neurotransmitter mechanisms controlling the lower urinary tract. The functions of the lower urinary tract to store and periodically eliminate urine are regulated by a complex neural control system in the brain, spinal cord, and peripheral autonomic ganglia that coordinates the activity of smooth and striated muscles of the bladder and urethral outlet. The neural control of micturition is organized as a hierarchical system in which spinal storage mechanisms are in turn regulated by circuitry in the rostral brain stem that initiates reflex voiding. Input from the forebrain triggers voluntary voiding by modulating the brain stem circuitry. Many neural circuits controlling the lower urinary tract exhibit switch-like patterns of activity that turn on and off in an all-or-none manner. The major component of the micturition switching circuit is a spinobulbospinal parasympathetic reflex pathway that has essential connections in the periaqueductal gray and pontine micturition center. A computer model of this circuit that mimics the switching functions of the bladder and urethra at the onset of micturition is described. Micturition occurs involuntarily in infants and young children until the age of 3 to 5 years, after which it is regulated voluntarily. Diseases or injuries of the nervous system in adults can cause the re-emergence of involuntary micturition, leading to urinary incontinence. Neuroplasticity underlying these developmental and pathological changes in voiding function is discussed.

Stability of the acetic acid-induced bladder irritation model in alpha chloralose-anesthetized female cats

Time- and vehicle-related variability of bladder and urethral rhabdosphincter (URS) activity as well as cardiorespiratory and blood chemistry values were examined in the acetic acid-induced bladder irritation model in α-chloralose-anesthetized female cats. Additionally, bladder and urethra were evaluated histologically using Mason trichrome and toluidine blue staining. Urodynamic, cardiovascular and respiratory parameters were collected during intravesical saline infusion followed by acetic acid (0.5%) to irritate the bladder. One hour after starting acetic acid infusion, a protocol consisting of a cystometrogram, continuous infusion-induced rhythmic voiding contractions, and a 5 min "quiet period" (bladder emptied without infusion) was precisely repeated every 30 minutes. Administration of vehicle (saline i.v.) occurred 15 minutes after starting each of the first 7 cystometrograms and duloxetine (1mg/kg i.v.) after the 8(th). Acetic acid infusion into the bladder increased URS-EMG activity, bladder contraction frequency, and decreased contraction amplitude and capacity, compared to saline. Bladder activity and URS activity stabilized within 1 and 2 hours, respectively. Duloxetine administration significantly decreased bladder contraction frequency and increased URS-EMG activity to levels similar to previous reports. Cardiorespiratory parameters and blood gas levels remained consistent throughout the experiment. The epithelium of the bladder and urethra were greatly damaged and edema and infiltration of neutrophils in the lamina propria of urethra were observed. These data provide an ample evaluation of the health of the animals, stability of voiding function and appropriateness of the model for testing drugs designed to evaluate lower urinary tract as well as cardiovascular and respiratory systems function.

Plasticity of urinary bladder reflexes evoked by stimulation of pudendal afferent nerves after chronic spinal cord injury in cats

Bladder reflexes evoked by stimulation of pudendal afferent nerves (PudA-to-Bladder reflex) were studied in normal and chronic spinal cord injured (SCI) adult cats to examine the reflex plasticity. Physiological activation of pudendal afferent nerves by tactile stimulation of the perigenital skin elicits an inhibitory PudA-to-Bladder reflex in normal cats, but activates an excitatory reflex in chronic SCI cats. However, in both normal and chronic SCI cats electrical stimulation applied to the perigenital skin or directly to the pudendal nerve induces either inhibitory or excitatory PudA-to-Bladder reflexes depending on stimulation frequency. An inhibitory response occurs at 3-10 Hz stimulation, but becomes excitatory at 20-30 Hz. The inhibitory reflex activated by electrical stimulation significantly (P<0.05) increases the bladder capacity to about 180% of control capacity in normal and chronic SCI cats. The excitatory reflex significantly (P<0.05) reduces bladder capacity to about 40% of control capacity in chronic SCI cats, but does not change bladder capacity in normal cats. Electrical stimulation of pudendal afferent nerves during slow bladder filling elicits a large amplitude bladder contraction comparable to the contraction induced by distension alone. A bladder volume about 60% of bladder capacity was required to elicit this excitatory reflex in normal cats; however, in chronic SCI cats a volume less than 20% of bladder capacity was sufficient to unmask an excitatory response. This study revealed the co-existence of both inhibitory and excitatory PudA-to-Bladder reflex pathways in cats before and after chronic SCI. However our data combined with published electrophysiological data strongly indicates that the spinal circuitry for both the excitatory and inhibitory PudA-to-Bladder reflexes undergoes a marked reorganization after SCI.

Urinary bladder function and somatic sensitivity in vasoactive intestinal polypeptide (VIP)-/- mice

Vasoactive intestinal polypeptide (VIP) is an immunomodulatory neuropeptide widely distributed in neural pathways that regulate micturition. VIP is also an endogenous anti-inflammatory agent that has been suggested for the development of therapies for inflammatory disorders. In the present study, we examined urinary bladder function and hindpaw and pelvic sensitivity in VIP(-/-) and littermate wildtype (WT) controls. We demonstrated increased bladder mass and fewer but larger urine spots on filter paper in VIP(-/-) mice. Using cystometry in conscious, unrestrained mice, VIP(-/-) mice exhibited increased void volumes and shorter intercontraction intervals with continuous intravesical infusion of saline. No differences in transepithelial resistance or water permeability were demonstrated between VIP(-/-) and WT mice; however, an increase in urea permeability was demonstrated in VIP(-/-) mice. With the induction of bladder inflammation by acute administration of cyclophosphamide, an exaggerated or prolonged bladder hyperreflexia and hindpaw and pelvic sensitivity were demonstrated in VIP(-/-) mice. The changes in bladder hyperreflexia and somatic sensitivity in VIP(-/-) mice may reflect increased expression of neurotrophins and/or proinflammatory cytokines in the urinary bladder. Thus, these changes may further regulate the neural control of micturition.

Maternal separation uncouples reflex from spontaneous voiding in rat pups

PURPOSE

Rat pups only void when the perigenital-bladder reflex is activated by the mother rat licking the perineum. Maternal separation causes bladder distention as well as stress responses and anxiety behaviors in adult rats. We determined if MS would change voiding reflex maturation in neonatal rats.

MATERIALS AND METHODS

A total of 14 Sprague-Dawley rat pups were subjected to 6 hours of daily MS and 17 were subjected to 6 hours of MS with bladder emptying by perigenital stimulation at 3 hours on postnatal days 2 to 14. Age matched controls for the 2 groups remained with the mother. Spontaneous voiding in awake pups from 1 to 3 weeks was monitored in a metabolic cage and perigenital-bladder reflex latency was determined from 1 to 7 weeks. Cystometry was performed at 9 weeks with the rats under urethane anesthesia.

RESULTS

Spontaneous voiding began at 3 weeks in all animals. The latency of the perigenital-bladder reflex at 3 weeks was shorter than the latency at 2 days in MS animals (3.3 vs 6.4 seconds, p < 0.01) but not in control or MSPG animals. MS animals maintained the perigenital-bladder reflex 2 weeks longer than control animals. The spontaneous voiding behavior of MSPG animals was similar to that in controls.

CONCLUSIONS

Intermittent bladder distention delays withdrawal of the spinal perigenital-bladder reflex but it does not affect maturation of the supraspinal bladder-bladder reflex that controls spontaneous voiding in older rats. This suggests that increased bladder afferent firing can selectively modulate spinal but not supraspinal mechanisms controlling postnatal changes in voiding function.

Plasticity in the injured spinal cord: can we use it to advantage to reestablish effective bladder voiding and continence?

Micturition is coordinated at the level of the spinal cord and the brainstem. Spinal cord injury therefore directly interrupts spinal neuronal pathways to the brainstem and results in bladder areflexia. Some time after injury, however, dyssynergic bladder and sphincter function emerges. The changes mediating the appearance of bladder function after spinal cord injury are currently unknown. Primary afferent neurons have been shown to sprout in response to spinal cord injury. Sprouting primary afferents have been linked to the pathophysiology of centrally manifested disorders, such as autonomic dysreflexia and neuropathic pain. It is proposed that sprouting of bladder primary afferents contributes to disordered bladder functioning after spinal cord injury. During development of the central nervous system, the levels of specific neuronal growth-promoting and guidance molecules are high. After spinal cord injury, some of these molecules are upregulated in the bladder and spinal cord, suggesting that axonal outgrowth is occurring. Sprouting in lumbosacral spinal cord is likely not restricted to neurons involved in the micturition reflex. Furthermore, sprouting of some afferents may be contributing to bladder function after injury, whereas sprouting of others might be hindering emergence of function. Thus selective manipulation of sprouting targeting afferents that are contributing to emergence of bladder function after injury is critical. Further research regarding the role that neuronal sprouting plays in the emergence of bladder function may contribute to improved treatment of bladder dyssynergia after spinal cord injury.

Distribution and fate of cocaine- and amphetamine-regulated transcript peptide (CARTp)-expressing cells in rat urinary bladder: a developmental study

We examined the distribution and fate of cocaine- and amphetamine-regulated transcript peptide (CARTp)(55-102)-immunoreactive (IR) structures in the neonatal and adult rat urinary bladder. Double-labeling studies examining CARTp with tyrosine hydroxylase (TH), neuronal nitric oxide synthase (nNOS), or choline acetyltransferase (ChAT) were performed in wholemounts of urothelium or detrusor or cryostat sections of the bladder. In younger animals (postnatal day [P]1, P3), CARTp-IR cell bodies in detrusor smooth muscle were observed in large clusters ( approximately 100 cells/cluster) at the ureteral insertion and along thick bundles of nerve fibers at the bladder base. The total number of CARTp-IR cells was significantly reduced (by five-fold) at P14, and this reduced number persisted into adulthood. The decrease in the number of CARTp-expressing cells was complemented with positive staining for cleaved caspase-3, suggesting that apoptosis contributed to this decrease. At birth (P1), all CARTp-IR cells expressed the neuronal marker Hu. After birth, CARTp was expressed by some neurons (CARTp-IR, Hu-IR) that represent intramural ganglion cells and by cells that lacked a neuronal phenotype (CARTp-IR, Hu-) but did express TH. Neither of these cell populations expressed ChAT immunoreactivity in adult bladder. These cells (CARTp-IR, Hu-, TH-IR) may represent paraganglion or small intensely fluorescent (SIF) cells. The percentage of colocalization of CARTp-IR and nNOS or TH was dependent on postnatal age and showed an inverse relationship. At P1, 67.1 % of CARTp-IR cells expressed nNOS immunoreactivity. Decreased colocalization was observed with increasing postnatal age. In contrast, 19.5% of CARTp-IR cells expressed TH at P1, but colocalization increased with postnatal age. The suburothelial plexus lacked CARTp-IR nerve fibers until P14, when nerve fibers with varicosities were observed in the urethra and bladder neck region. In summary, we demonstrate 1) a decrease in the number of CARTp-IR cells in rat detrusor in early postnatal development; 2) apoptotic events in the bladder during early postnatal development; 3) rostral migration of CARTp-IR cells from the ureteral insertion toward the bladder body during postnatal development; 4) the presence of different populations of CARTp-IR cells, some with and others without a neuronal phenotype; and (5) age-dependent changes in chemical coding of CARTp-IR cells with postnatal development. This study demonstrates that CARTp-IR intramural ganglia and CARTp-IR paraganglion or SIF cells exist in the postnatal and adult rat bladder, although the role of these cell types remains to be determined.

Corticotropin-releasing factor (CRF) expression in postnatal and adult rat sacral parasympathetic nucleus (SPN)

The neural control of micturition undergoes marked changes during the early postnatal development. During the first few postnatal weeks, the spinal micturition reflex is gradually replaced by a spinobulbospinal reflex pathway that is responsible for micturition in adult animals. Upregulation of brainstem regulation of spinal micturition pathways may contribute to development of mature voiding patterns. We examined the expression of corticotropin-releasing factor (CRF), present in descending projections from Barrington's nucleus to the sacral parasympathetic nucleus (SPN), in postnatal (P0-P36) and adult Wistar rats (P60-90). CRF-immunoreactivity (IR) was present predominantly in the SPN region, although some staining was also observed in the dorsal horn and dorsal commissure in L5-S1 spinal segments. CRF-IR in spinal cord regions was age dependent (R2=0.87-0.98). The majority of the CRF-IR in the lumbosacral spinal cord was eliminated by complete spinalization (2-3 weeks). Double-label immunohistochemistry was combined with quantitative confocal laser scanning microscopy to quantify the number and percentage of colocalization between CRF-immunoreactive varicosities and preganglionic somas or proximal neurites in the SPN in postnatal and adult rats. Results demonstrate an age-dependent upregulation of CRF-IR in the SPN region and specifically in association with preganglionic parasympathetic neurons identified with neuronal nitric oxide synthase (nNOS)-IR. CRF-immunoreactive varicosities on or within a 1 microm perimeter of nNOS-immunoreactive somas or proximal neurites also increased with postnatal age. The upregulation of CRF-IR in bulbospinal projections to the SPN may contribute to mature voiding reflexes.

Localization of P2X and P2Y Receptors in Dorsal Root Ganglia of the Cat

The distribution of P2X and P2Y receptor subtypes in upper lumbosacral cat dorsal root ganglia (DRG) has been investigated using immunohistochemistry. Intensity of immunoreactivity for six P2X receptors (P2X5 receptors were immuno-negative) and the three P2Y receptors examined in cat DRG was in the order of P2Y2 = P2Y4>P2X3>P2X2 = P2X7>P2X6>P2X1 = P2X4>P2Y1. P2X3, P2Y2, and P2Y4 receptor polyclonal antibodies stained 33.8%, 35.3%, and 47.6% of DRG neurons, respectively. Most P2Y2, P2X1, P2X3, P2X4, and P2X6 receptor staining was detected in small- and medium-diameter neurons. However, P2Y4, P2X2, and P2X7 staining was present in large- and small-diameter neurons. Double-labeling immunohistochemistry showed that 90.8%, 32.1%, and 2.4% of P2X3 receptor-positive neurons coexpressed IB4, CGRP, and NF200, respectively; whereas 67.4%, 41.3%, and 39.1% of P2Y4 receptor-positive neurons coexpressed IB4, CGRP, and NF200, respectively. A total of 18.8%, 16.6%, and 63.5% of P2Y2 receptor-positive neurons also stained for IB4, CGRP, and NF200, respectively. Only 30% of DRG neurons in cat were P2X3-immunoreactive compared with 90% in rat and in mouse. A further difference was the low expression of P2Y1 receptors in cat DRG neurons compared with more than 80% of the neurons in rat. Many small-diameter neurons were NF200-positive in cat, again differing from rat and mouse.

Overactive bladder and incontinence in the absence of the BK large conductance Ca2+-activated K+ channel

BK large conductance voltage- and calcium-activated potassium channels respond to elevations in intracellular calcium and membrane potential depolarization, braking excitability of smooth muscle. BK channels are thought to have a particularly prominent role in urinary bladder smooth muscle function and therefore are candidate targets for overactive bladder therapy. To address the role of the BK channel in urinary bladder function, the gene mSlo1 for the pore-forming subunit of the BK channel was deleted. Slo(-/-) mice were viable but exhibited moderate ataxia. Urinary bladder smooth muscle cells of Slo(-/-) mice lacked calcium- and voltage-activated BK currents, whereas local calcium transients ("calcium sparks") and voltage-dependent potassium currents were unaffected. In the absence of BK channels, urinary bladder spontaneous and nerve-evoked contractions were greatly enhanced. Consistent with increased urinary bladder contractility caused by the absence of BK currents, Slo(-/-) mice demonstrate a marked elevation in urination frequency. These results reveal a central role for BK channels in urinary bladder function and indicate that BK channel dysfunction leads to overactive bladder and urinary incontinence.

Developmental changes in spontaneous smooth muscle activity in the neonatal rat urinary bladder

Changes in spontaneous activity of the urinary bladder during postnatal development were examined in muscle strips from the base and dome of bladders from 1- to 5-wk-old rats. Activity was analyzed using fast Fourier transformation (FFT), nonlinear cross prediction, and the Shannon entropy test. Spontaneous activity was not detected in strips from 1- to 5-day-old rats but was observed in 50% of strips from 6- to 7-day-old rats and was prominent in strips from 2-wk-old animals. FFT analysis revealed one peak in activity, which was significantly faster in the bladder base (0.21 +/- 0.03 Hz) than in the dome (0.08 +/- 0.01 Hz). A second peak at approximately 0.5 Hz was detected at 3-5 wk of age. Atropine but not tetrodotoxin decreased the amplitude of spontaneous contractions, whereas carbachol, a muscarinic agonist, unmasked or stimulated spontaneous activity. These data suggest that slow rhythmic activity observed previously in neonatal whole bladders is generated by pacemaker cells in the bladder base or dome. The emergence of faster activity in bladders from older animals may reflect the development of multiple pacemaker sites, which would reduce coordination within the bladder wall and improve storage function in the mature bladder.

Transient neonatal expression of NR2B/2D subunit mRNAs of the N-methyl-D-aspartate receptor in the parasympathetic preganglionic neurons in the rat spinal cord

Physiological studies have shown that lower urinary tract function is regulated through glutamate receptors at the levels of spinal and supraspinal cord. Of the receptor family, N-methyl-D-aspartate (NMDA) receptors mediate activity-dependent changes of synaptic efficacy, underlying synaptic plasticity and synapse development. To know the ontogenic changes of NMDA receptor expression in the visceromotor system innervating pelvic organs, including the bladder, we employed double labeling technique of retrograde neuronal tracing and in situ hybridization for detecting NMDA subunit mRNAs in preganglionic neurons (PGNs) of the lumbosacral cord. Rats at postnatal day 7 (P7), 14 (P14), 21 (P21), and adult were used. In situ hybridization was conducted using 35S-labeled antisense oligonucleotides specific to mRNAs for NMDA receptor subunits. Hybridizing signals in PGNs were detected by a dark-field microscope equipped fluorescence detector. PGNs showed strong signals for NR1 subunit mRNA at each developmental stage examined. Moderate signals for the NR2B and NR2D subunit mRNAs were found in PGNs at P7. However, their expression levels decreased thereafter, reaching the minimal level in adults. No significant signals for NR2A and NR2C subunit mRNAs were detected at any stages. This temporal pattern of expression suggests a possible involvement of NMDA receptors in the development of micturitional neural circuit through activity-dependent mechanisms.

Inhibitory control of the urinary bladder in the neonatal rat in vitro spinal cord-bladder preparation

Urinary bladder activity of the neonatal rat is tonically inhibited by neural input from the spinal cord passing through axons in the pelvic nerve. The present study was undertaken to examine the organization of this inhibitory mechanism using in vitro spinal cord-bladder preparations of neonatal rats in which the lumbosacral dorsal roots (DRs) or ventral roots (VRs) were transected. Isovolumetric bladder contractions occurring spontaneously or induced by electrical stimulation of the bladder wall (ES-BW) were measured. In DR transected (DRT) preparations, removal of the spinal cord significantly enhanced (50-59%) the amplitude of spontaneous and ES-BW-evoked bladder contractions; whereas in VR transected (VRT) preparations removal of the spinal cord produced only a small enhancement (6.7-12%). However, in VRT preparations, electrical stimulation of the dorsal roots reduced the amplitude of spontaneous contractions, an effect blocked by a nicotinic ganglionic blocking agent, hexamethonium. In DRT preparations, MK-801 enhanced the amplitude of spontaneous and ES-BW-evoked contractions. These results demonstrate that bladder activity of the neonatal rat is tonically inhibited by input from the lumbosacral spinal cord via parasympathetic pathways in the pelvic nerve. The inhibitory outflow is not dependent upon afferent input to the cord but is facilitated by NMDA glutamatergic transmission in the spinal cord. Antidromic activation of afferent axons also appears to induce inhibition in the bladder via a mechanism involving nicotinic cholinergic receptors. These findings suggest that spinal and peripheral inhibitory mechanisms may play an important role in controlling voiding in the neonatal rat.

Developmental expression of urinary bladder neurotrophic factor mRNA and protein in the neonatal rat

These studies were performed to determine the developmental expression pattern of neurotrophic factor (NTF: nerve growth factor (betaNGF), brain-derived neurotrophic factor (BDNF), glial-derived neurotrophic factor (GDNF), ciliary neurotrophic factor (CNTF), neurotrophin-3 (NT-3) and NT-4 mRNA and NGF, NT-3 and NT-4 protein in the urinary bladder of the postnatal Wistar rat. It was hypothesized that NTFs may contribute to the development of the spinobulbospinal micturition reflex that represents the adult micturition pattern. Changes in NTF mRNA or protein expression in the urinary bladder at the time of development of the mature micturition reflex (postnatal days (P) 16-18) may suggest an involvement of target-derived NTFs in this maturation process. Developmental ages, prior to (P5, P10, P15) or following (P20, P30, adult P90) the development of the spinobulbospinal micturition reflex were selected and the urinary bladder was analyzed for levels of neurotrophic factor mRNA or protein. Results from ribonuclease protection assays demonstrated a similar developmental pattern among each neurotrophic factor examined. Neurotrophic factor mRNA levels increased by P10 and reach a maximum by P15. Subsequently, NTF mRNA levels declined to adult levels that were less than the earliest postnatal time examined (P5). NTF mRNA expression was significantly (p</=0.05-0.001) greater at P10, P15, P20 and P40 (NT-4 mRNA) compared to adult levels for each NTF examined except GDNF mRNA. In general, NGF, NT-3 and NT-4 urinary bladder protein levels in early postnatal development, as determined by ELISA, were similar when compared to the corresponding mRNA expression. Differences in the correlation between NT-3 and NT-4 mRNA and protein expression were demonstrated in the adult urinary bladder where significantly (p</=0. 001) greater levels of protein were revealed despite relatively low abundance of NT-3 and NT-4 mRNA. The developmental expression pattern (maximum expression at the second to third postnatal week) of NTFs in the urinary bladder is consistent with a potential role in the development of the spinobulbospinal reflex. Relatively high expression of NT-3 and NT-4 protein in the adult urinary bladder suggests a potential importance of these factors in the adult lower urinary tract.

Maturation of bladder reflex pathways during postnatal development

Neuroanatomical and electrophysiological techniques have provided new insights into the organization of the spinal cord circuitry and the neurotransmitter mechanisms involved in primitive voiding reflexes in neonatal animals. In addition, studies of unitary synaptic transmission in spinal cord slice preparations indicate that developmental and spinal cord injury induced plasticity in sacral parasympathetic reflex pathways is due in part to alterations in glutamatergic excitatory transmission between interneurons and parasympathetic preganglionic neurons. It is proposed that these synaptic changes are due to competition between segmental and supraspinal inputs. Thus synaptic remodeling in the sacral parasympathetic nucleus is likely to be an important factor in the postnatal maturation of voiding reflexes.

Influence of temperature on activity of the isolated whole bladder preparation of neonatal and adult rats

The temperature sensitivity of in vitro whole bladder preparations from neonatal and adult rats with or without chronic partial urethral obstruction was investigated. After the bladder was filled to a volume eliciting isovolumetric contractions, temperature was changed between 19 and 38 degrees C. In all preparations, higher temperatures were associated with higher frequencies of spontaneous intravesical pressure waves (IVPW). In 1- to 2-wk-old neonates, IVPW amplitude increased as the temperature increased; however, in older neonates and normal adults, the opposite occurred. The transition period was at 3 wk of age when bladder volume also markedly increased. At this age as well as in adult rats with outlet obstruction, changing temperature had little influence on the amplitude of IVPW. Thus obstructed outlet bladders and 3-wk-old bladders had similar properties. It is concluded that the properties of bladder muscle are changed during postnatal maturation and that in 3-wk-old rats, when brain control of voiding is emerging, micturition is abnormal, leading to obstructive changes in bladder muscle.

Developmental aspects of endothelin receptors in rabbit lower urinary tract

Since evidence of development/age-related alterations of endothelin receptors in circulation and respiration systems has been increasing, we attempted to investigate the pharmacological characterization of endothelin receptors in neonatal, premature, and mature male rabbit lower urinary tract. The biochemical properties of ET receptors were examined in the lower urinary tracts of 1-day (neonatal)-, 6-week (premature)-, and 1-year(mature)-old male rabbits with binding technique utilizing [(125)I]ET-1. The rank orders of the densities (B(max) values) of endothelin receptors in the bladder dome, bladder base, and urethra of different aged rabbits were bladder dome, 1 day > 6 week &vbar;Ls 1 year, bladder base, 1 day > 6 week &vbar;Ls 1 year, and urethra, 1 day > 6 week > 1 year. The pharmacological profiles of these binding sites inhibited by various kinds of endothelin receptor compounds showed similar K(i) values and similar proportions of endothelin receptor subtypes in the same regions of 1-day-, 6-week-, and 1-year-old animals. Our data clearly demonstrated the presence of regional difference and development-related changes in the density and subtype specificity of endothelin receptors in the lower urinary tract of the male rabbit. Neurourol. Urodynam. 19:71-85, 2000.

Sacral spinal cord neurons responsive to bladder pelvic and perineal inputs in cats

In chloralose-anesthetized or decerebrate male cats, 70% of 73 sacral spinal cord neurons activated from the bladder branch of the pelvic nerve also received excitatory inputs from urethra and/or perineal cutaneous nerves (sensory pudendal in 55% and superficial perineal in 84% of neurons). Only 29% of these neurons were excited by the hindlimb skin and muscle nerves tested. The pelvic nerve-responsive neurons received monosynaptic urethral/perineal input in 25% of cases and required temporal summation of this input in 47% of cases. Of 211 neurons responding to superficial perineal nerve stimulation, 101 were not excited by the other nerves tested. Neurons activated by superficial perineal nerve stimulation were found predominantly in S2. It is likely that the superficial perineal nerve represents an important pathway whereby perineal stimulation influences bladder function.

Developmental and injury induced plasticity in the micturition reflex pathway

The storage and periodic elimination of urine are dependent upon neural circuits in the brain and spinal cord that co-ordinate the activity of the urinary bladder, the urethra and the striated urethral sphincter. This study utilized anatomical, electrophysiological and pharmacological techniques to examine: (1) the organization of the parasympathetic excitatory reflex mechanisms that control the urinary bladder of the rat and the cat; and (2) the changes in these reflexes during postnatal development and after spinal cord injury. In normal adult cats and rats, the parasympathetic excitatory input to the bladder is dependent upon a spinobulbospinal reflex pathway that is activated by myelinated (Adelta) bladder afferents and that passes through an integrative center (the pontine micturition center, PMC) in the rostral brain stem. Transneuronal tracing studies using pseudorabies virus as well as physiological methods have revealed that the PMC is located in close proximity to the locus coeruleus. Single unit recordings indicate that neurons in the PMC respond to afferent input from the bladder and are excited prior to or during reflex bladder contractions. Glutamic acid is the major excitatory transmitter in the micturition reflex pathway. Glutamatergic transmission which is mediated by AMPA/kainate and NMDA receptors can be modulated by a variety of other transmitters. In neonatal animals, a spinal micturition reflex is activated by somatic afferent fibers from the perigenital region. This reflex is suppressed during postnatal development, but can be unmasked in adult animals following spinal cord injury. Spinal injury also causes the emergence of a spinal bladder-to-bladder reflex which in the cat is activated by capsaicin-sensitive C-fiber bladder afferents. Patch clamp studies in spinal cord slice preparations indicate that developmental and spinal cord injury induced plasticity in sacral parasympathetic reflex pathways is due in part to alterations in glutamatergic excitatory transmission between interneurons and preganglionic neurons. Changes in the electrical properties of bladder afferent pathways may also contribute to the reorganization of bladder reflexes in paraplegic animals.

Developmental synaptic depression underlying reorganization of visceral reflex pathways in the spinal cord

During development, neuronal connectivity has a remarkable plasticity. Synaptic refinement in the spinal autonomic nucleus might be involved in the elimination of primitive segmental reflexes and the emergence of mature spinobulbospinal reflexes, which occurs a few weeks after birth. To address this possibility, we examined the postnatal changes of segmental excitatory synaptic transmission by applying the whole-cell recording technique to parasympathetic preganglionic neurons in slice preparations of the rat lumbosacral spinal cord. The mean magnitude of unitary excitatory synaptic currents evoked in preganglionic neurons by stimulation of single interneurons remained unchanged during the first two postnatal weeks but was reduced by 50% during the third postnatal week. This reduction in synaptic efficacy was associated with a decrease in the amount of transmitter release from interneurons. Moreover, this developmental depression of segmental synaptic transmission was prevented by spinal cord transection at the thoracic level on postnatal day 14. Thus, developmental modification of excitatory synapses on preganglionic neurons appears to be attributable to competition between segmental interneuronal and descending bulbospinal inputs, which results in the developmental reorganization of parasympathetic excretory reflex pathways.

The central neural pathways involved in micturition in the neonatal rat as revealed by the injection of pseudorabies virus into the urinary bladder

Pseudorabies virus was injected into the wall of the urinary bladder in 2- and 12-day-old rats in order to examine developmental changes in the central neural pathways controlling micturition. Forty-eight hours after virus injection, virus-labeled neurons were identified in the lumbosacral spinal cord but not in the brain. Sixty to seventy-two hours after virus injection in both 2- and 12-day-old rats, infected neurons were detected in Barrington's nucleus, nucleus paragigantocellularis, nucleus reticularis gigantocellularis, A5 area, nucleus raphe obscurus, locus subcoeruleus, periaquaductal gray, red nucleus, paraventricular nucleus and cerebral cortex. These results in neonatal rats are similar to those reported in adult rats. Thus, it is likely that the supraspinal neural circuitry which underlies micturition in the adult animal is already organized in the neonatal rat during the early postnatal period even though the supraspinal micturition reflex pathway does not become functional until the third postnatal week.

Some new insights into bladder function in infancy

OBJECTIVES

To evaluate normal bladder function and micturition patterns in infants.

PATIENTS, SUBJECTS AND METHODS

Twenty-one infants (16 boys, five girls; mean age 5.9 months) with no lower urinary tract pathology underwent natural filling cystometry. Micturition patterns were also observed simultaneously with polysomnography in 26 healthy neonates (16 boys, 10 girls; mean age 7.4 days).

RESULTS

In infants, cystometry showed (95% CI) a capacity of 42-53 mL, a maximum rise in detrusor pressure during voiding of 95-120 cmH2O and a voiding efficiency (voided volume/capacity) of 0.86-0.91. On micturition, urinary flow was discoordinated from peak detrusor pressures in 10 infants. Detrusor instability occurred in one of 21 infants. Micturition was observed only during wakefulness or on arousal from sleep. In neonates, 17 of 61 recorded voids (28%) were during full wakefulness and 44 (72%) during arousal from sleep. Notably, none of the recorded voids occurred during quiet sleep.

CONCLUSIONS

The normal infant's bladder was stable and emptied almost completely. Voiding with incomplete co-ordination between detrusor contraction and urinary sphincter relaxation could be normal. Micturition never occurred during quiet sleep. There was cortical arousal in response to a full bladder even in new-born infants. This contradicts the traditional concept of a totally uninhibited bladder in infancy. There are potential implications for the management of children with nocturnal enuresis.

Detrusor-sphincteric dyssynergia in paraplegics compared with the synergia in a brain-dead human by using the single-fibre action potential recording method

(1) Humans with spinal cord lesions often show detrusor-sphincteric dyssynergia of the urinary bladder which is reflected urodynamically in the detrusor pressure and a simultaneous increase in electromyographic pelvic floor activity. (2) The time-course of the increase in the secondary muscle spindle afferent activity, induced by the parasympathetic nervous system in muscle spindles contributing to continence, is very similar to that of detrusor pressure. The detrusor-sphincteric dyssynergia is therefore analysed by comparing the natural impulse patterns of secondary muscle spindle afferents (SP2) and sphincteric motoneurons in a brain-dead human with those in patients with spinal cord lesion. The parasympathetic nervous system was activated by painful bladder catheter pulling. (3) In a brain-dead human the sphincteric motoneurons subserving continence were inhibited at a time, when preganglionic parasympathetic efferents increased their activity for 10 s and an SP2 fibre increased its activity for several minutes. In a paraplegic with a strong bladder dysfunction, the SP2 fibre activity increased, due to parasympathetic activation, lasted for approx. 1 min, showed undulations and its amplitude was smaller than that measured in a brain-dead human. The sphincteric motoneurons were not inhibited. (4) In the brain-dead human, an SP2 fibre showed doublet firing with interspike intervals (IIs) of a duration between 10 and 14 ms for low level parasympathetic activation. For high level parasympathetic activation this single parent spindle afferent fibre showed multi-ending regular firing of up to 6 endings with IIs of a duration of predominantly 15 to 25 ms. In one paraplegic with a strong bladder dysfunction the doublet firing was less regular, even though two II peaks at 10.2 and 11.2 ms occurred in a II distribution similar to the brain-dead human. The multi-ending regular firing was replaced by a repeated burst firing. In a second paraplegic with strong detrusor-sphincteric dyssynergia the burst firing consisted of up to 6 impulses with increasing IIs and a first II of approx. 0.2 ms (transmission frequency 5000 Hz). In a third paraplegic with a lesser dysfunction of the bladder a highly activated SP2 fibre showed an activity pattern intermediate to those of multi-ending regular firing and burst firing. (5) The time constant for the activity decrease of a spindle afferent fibre following parasympathetic activation was to 31 s in a paraplegic and approx. 40 s in a brain-dead human. It is concluded that the muscle spindles are unchanged following spinal cord lesion.(ABSTRACT TRUNCATED AT 400 WORDS)

Pelvic and pudendal reflexes in the in vitro neonatal rat preparation

Pudendal-to-pelvic and pudendal-to-pudendal reflexes are described in an in vitro brainstem-spinal cord neonatal rat preparation. Cystometrograms and peripheral pelvic nerve recordings were used to monitor excitatory micturition reflexes evoked by tactile perineal stimulation or by continuous electrical stimulation of the sensory pudendal nerve. Micturition was characterized by an increased bladder pressure and a period of tonic pelvic nerve activity during which time fluid was expelled from the urethra. Single stimuli delivered to the sensory pudendal nerve evoked a phasic response in the pelvic nerve (pudendal-to-pelvic reflex) or pudendal motor nerve (pudendal-to-pudendal reflexes). The pudendal-to-pelvic reflex consisted of a single response occurring after a mean latency of 98 +/- 24 ms. The pudendal-to-pudendal reflex was comprised of two responses, the first occurred at a mean latency of 105 +/- 11 ms and the second at 383 +/- 36 ms. Cervical or lower thoracic spinal transection did not alter the pudendal-to-pelvic reflex, however, the second component of the pudendal-to-pudendal reflex was abolished. The use of preganglionic pelvic and pudendal peripheral nerve recordings described in this study provide a direct measure of the reflex outflow from the CNS and can be used to examine developmental changes and neurochemical substrates within the CNS which contribute to micturition and coital reflexes in the rat.

Role of glutamate and NMDA receptors in the descending limb of the spinobulbospinal micturition reflex pathway of the rat

MK-801, an NMDA receptor antagonist administered intravenously or intrathecally to the L6-S1 spinal cord inhibited in a dose dependent manner the amplitude of isovolumetric bladder contractions evoked by electrical stimulation in the pontine micturition center (PMC) in urethane anesthetized rats. The mean threshold dose of MK-801 was 10 +/- 6 micrograms/kg i.v. and 10 +/- 1 micrograms i.t. Bladder contractions were completely inhibited at doses ranging from 300 to 3000 micrograms/kg i.v. and from 18 to 48 micrograms i.t. These data indicate that NMDA glutamatergic receptors play an important role in excitatory transmission in the descending pathway from the PMC to the spinal segmental circuitry involved in the control of the urinary bladder.

Ontogeny of nitric oxide synthase in the lumbosacral spinal cord of the neonatal rat

The present experiments were performed to determine the temporal pattern of expression of nitric oxide synthase (NOS) immunoreactivity in cells and fibers in the lumbosacral spinal cord during early postnatal development and to examine the relationship between NADPH-diaphorase (NADPH-d) activity and NOS-immunoreactivity (IR). At postnatal days 0-1 and 4-5, NADPH-d and NOS-IR were detected in L6-S1 segments of the spinal cord in cells and fibers in the region of the sacral parasympathetic nucleus (SPN), dorsal commissure and around the central canal but were absent in the superficial layers of the dorsal horn. Fiber staining on the lateral edge of the dorsal horn (the lateral collateral pathway, LCP) in a region containing primary afferent projections from the pelvic viscera and in a fiber tract in the dorsolateral funiculus was also not detectable. At days 4-5 some stained cells were detected in the deeper laminae of the dorsal horn. At postnatal days 10-12 and 20-22, cells in the region of the SPN, around the central canal and in the superficial laminae of the dorsal horn exhibited NADPH-d and NOS-IR. NADPH-d and NOS-IR fiber staining in the superficial laminae of the dorsal horn and the dorsolateral funiculus was observed at postnatal days 10-12 and increased in staining intensity by postnatal days 20-22. NADPH-d fiber staining in the LCP was not prominent at postnatal days 10-12; however, prominent fiber staining at this site did occur by postnatal days 20-22 and in adult animals. In postnatal days 20-22 and in adult animals NADPH-d activity and NOS-IR had a similar distribution except in the LCP where NADPH-d stained fibers did not exhibit NOS-IR. These data indicate that NADPH-d and NOS-IR in the spinal cord exhibit marked changes during the early postnatal development. The changes in afferent projections in the LCP may be related to maturation of visceral reflex pathways including micturition.

Effects of MK-801 and CNQX, glutamate receptor antagonists, on bladder activity in neonatal rats

This study was undertaken to examine the role of N-methyl-D-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) glutamatergic receptors in the regulation of urinary bladder activity in the neonatal rat. Experiments were conducted using an in vitro spinal cord-bladder (SB) preparation from 1- to 5-day-old rats or awake neonatal rats 6 and 7 days old. SB preparations were isolated under hypothermic anesthesia. Isovolumetric bladder contractions occurred spontaneously, were induced by electrical stimulation (ES) of the bladder wall or were evoked reflexly by perineal tactile stimulation (PS). MK-801 (3-30 microM), an NMDA receptor antagonist, enhanced the amplitude of spontaneous, ES- and PS-evoked contractions. Removal of the spinal cord after MK-801 abolished PS-evoked reflex contractions but did not change the amplitude of spontaneous and ES-evoked contractions. Removal of the spinal cord in the absence of MK-801 increased the amplitude of spontaneous and ES-evoked contractions, indicating that the bladder is subject to a tonic inhibitory control originating in the spinal cord. 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 3-30 microM), an AMPA receptor antagonist, decreased the amplitude of PS-evoked contractions and the frequency of spontaneous contractions in the SB preparation. Removal of the spinal cord after CNQX enhanced the amplitude of spontaneous and ES-evoked contractions but abolished PS-evoked contractions. The frequency of spontaneous contractions which decreased after CNQX increased to near control levels after removal of the spinal cord. In awake neonatal rats, intraperitoneal injection of MK-801 (3 mg/kg) induced spontaneous micturition. A large dose of CNQX (30 mg/kg) decreased PS-evoked micturition volume. These results suggest that NMDA glutamatergic receptors are involved in a lumbosacral spinal inhibitory mechanism controlling bladder activity; whereas AMPA glutamatergic receptors are involved in the perineal-to-bladder reflex pathway in neonatal rats.

Rat: overview and innervation

Despite the development of molecular and cellular methods for examining physiological processes, the use of the whole animal model remains essential to advance knowledge regarding the integration and coordination of events associated with urinary tract function. The rat offers an inexpensive and versatile species to investigate bladder and urethral responses to drugs or pathology. Models for many disorders have been developed in rodents including diabetes, multiple sclerosis, spinal cord injury, Parkinson's disease, bladder outlet obstruction, pain, and aging. This review examines methodologies to evaluate lower urinary tract function and manipulations used to create pathological models in rodents.

Spinal pathways mediate coordinated bladder/urethral sphincter activity during reflex micturition in decerebrate and spinalized neonatal rats

Coordination between the urinary bladder and the external urethral sphincter is necessary for normal voiding. However, it is uncertain whether the spinal cord or brainstem generates this coordination. Bladder and urethral sphincter activity were examined during reflex voiding induced by perineal stimulation or bladder distension in decerebrate non-spinalized and spinalized 15 to 26-day-old neonatal rats. Perineal stimulation induced voiding and coordinated bladder/sphincter activity in both types of rats, indicating that spinal pathways can generate coordinated voiding behavior. The discoordination observed during voiding induced by bladder distension in spinalized pups may be due to the loss of descending pathways or to the emergence of detrimental spinal reflexes.

Postnatal development of opioid regulation of micturition in the kitten

Endogenous opioids tonically regulate micturition in adult mammals. The present study sought to determine if opioids regulate micturition in neonatal kittens. Naloxone (up to 2 mg/kg given i.p. or i.v. to unanesthetized/ketamine-anesthetized or chloralose-anesthetized kittens, respectively), an opioid receptor antagonist, produced no effects in unanesthetized, ketamine-anesthetized, or chloralose-anesthetized kittens that had been prepared for bladder pressure recording, until 3 weeks of age. This indicates that endogenous opioids are not tonically regulating micturition in neonatal kittens. From 3 weeks up to at least 6 weeks of age, naloxone (100 micrograms/kg i.p. or i.v.) weakly facilitated bladder activity by transiently increasing the amplitude and/or duration of bladder contractions, but no effects on frequency of contractions was recorded. Morphine (up to 2 mg/kg given i.p. or i.v. to unanesthetized/ketamine-anesthetized or chloralose-anesthetized kittens, respectively), an opioid agonist, did not inhibit bladder contractions in unanesthetized or ketamine-anesthetized neonatal kittens, but it did inhibit (at a threshold dose of 100 micrograms/kg) and completely abolished (at a dose of 300 micrograms/kg) bladder activity in chloralose-anesthetized kittens in a dose-dependent, naloxone-reversible manner. Surprisingly, following morphine administration to unanesthetized or ketamine-anesthetized neonatal kittens, naloxone now produced an adult-like enhancement of bladder activity. These latter results indicate that opioid receptors, whose inhibitory effects are anesthetic-dependent, are present along the micturition reflex pathway in neonates. Immunohistochemical studies of the sacral spinal cord revealed that opioid peptides are distributed similarly in neonatal and adult cats.

Mechanisms underlying the recovery of urinary bladder function following spinal cord injury

Micturition in cats and rats with an intact neuraxis is dependent upon a spinobulbospinal reflex activated by A delta bladder afferents. This report describes changes in micturition reflexes 2 h to 14 weeks following spinal cord transection at the lower thoracic level. In acute spinal cats micturition reflexes were blocked, however, several weeks after transection, a long latency (180-200 ms) spinal reflex could be activated by C-fiber bladder afferents. This reflex was blocked by capsaicin in doses (20-30 mg/kg, s.c.) that did not affect micturition reflexes in intact cats. Micturition reflexes were unmasked in acute spinal and facilitated in chronic spinal cats by naloxone, an opioid antagonist. Spinal neurons and axons containing opioid peptides were more prominent below the level of transection in chronic spinal cats. VIP, a putative neurotransmitter in C-fiber bladder afferents, inhibited micturition reflexes when injected intrathecally (2-10 micrograms) in intact cats but facilitated micturition reflexes in spinal cats (doses 0.1-1 micrograms, i.t.). VIP-containing C-fiber afferent projections to lamina I of the sacral spinal cord expanded in spinal cats. Thus VIP afferents may have an important role in the recovery of bladder reflexes after spinal injury. Paraplegic animals also exhibit bladder-sphincter dyssynergia, which causes functional outlet obstruction. Studies in rats have revealed that outlet obstruction induced by partial urethral ligation facilitates spinal micturition reflex pathways and causes an expansion of HRP-labelled bladder afferent projections in the spinal cord. These findings raise the possibility that the alterations in central reflex connections in paraplegic animals may be induced in part by changes in peripheral afferent input secondary to outlet obstruction.(ABSTRACT TRUNCATED AT 250 WORDS)

Unmasking of a neonatal somatovesical reflex in adult cats by the serotonin autoreceptor agonist 5-methoxy-N,N-dimethyltryptamine

In neonatal kittens, micturition is induced by a spinal somatovesical reflex pathway that is activated by the mother cat licking the perigenital region of the kitten. The somatovesical reflex pathway disappears about the time of weaning and is replaced by a vesicovesical reflex pathway that produces micturition via a supraspinal reflex pathway that is activated by distension of the urinary bladder. Furthermore, stimulation of the perigenital region in adult cats actually inhibits the supraspinal vesicovesical micturition reflex. Spinalization prompts the return of the somatovesical reflex, immediately in weaned kittens but over a course of days to weeks in adult cats. The purpose of the present experiments was to determine if the somatovesical reflex could be demonstrated acutely, and reversibly, in adult cats with an intact spinal cord via pharmacological suppression of the serotonergic system. The serotonergic system was suppressed by the intravenous administration of 5-methoxy-N,N-dimethyltryptamine (5-MeODMT), a serotonin agonist that inhibits the firing of serotonergic neurons via activation of inhibitory somatodendritic autoreceptors. 5-MeODMT in low doses (20-50 micrograms/kg) abolished inhibition of the bladder produced by either light tactile stimulation of the perigenital region or by electrical stimulation of the pudendal nerve, which carries the afferent fibers from the perigenital region, in 9 of 10 adult cats. Furthermore, in 8 of the 10 cats, the bladder inhibition was reversed to an excitation of variable amplitudes in each cat. Higher doses of 5-MeODMT (100-1000 micrograms/kg) abolished spontaneous bladder activity but did not inhibit perigenital-induced bladder contractions in those 8 animals in which the drug unmasked the excitatory somatovesical reflex.(ABSTRACT TRUNCATED AT 250 WORDS)