Activation of the external urethral sphincter central pattern generator by a 5-HT(1A) receptor agonist in rats with chronic spinal cord injury

We recently demonstrated that treatment with the 5-HT(1A/7) receptor agonist [(R)-(+)-8-hydroxy-2-di-n-propylamino]tetralin (8-OH-DPAT) increases bladder capacity in chloralose-anesthetized female cats with chronic spinal cord injury. In the current study, we investigated the effects of 8-OH-DPAT on bladder capacity and external urethral sphincter (EUS) activity in urethane-anesthetized female rats (initial body mass 175-200 g) with chronic spinal cord injury (transsection at T10). Cystometric study took place 8-12 wk posttranssection. Intravesical pressure was monitored in urethane-anesthetized rats with a transvesical catheter, and EUS activity was assessed electromyographically. Spinal cord injury disrupts phasic activity of the EUS, resulting in decreased voiding efficiency and increased residual volume. 8-OH-DPAT induced a dose-dependent decrease in bladder capacity (the opposite of its effect in chronic spinal cord-injured cats) with an increase in micturition volume and decrease in residual volume resulting from improvement in voiding efficiency. The unexpected improvement in voiding efficiency can be explained by the 8-OH-DPAT-induced emergence of phasic EUS relaxation. Phasic EUS relaxation was also altered by 8-OH-DPAT in spinally intact rats, whereas the 5-HT(1A) receptor antagonist N-tert-butyl-3-[4-(2-methoxyphenyl)-piperazin-1-yl]-2-phenylpropanamide (WAY-100635), on its own, was without effect. It remains to be determined when phasic relaxation is restored after spinal cord injury, and indeed whether it is ever truly lost or is only temporarily separated from excitatory input.     

Increased spinal expression of c-Fos following stimulation of the lower urinary tract in chronic spinal cord-injured rats

c-Fos expression was studied in the lumbar and sacral spinal cord regions involved in processing afferent input from the lower urinary tract and a comparison was made between spinal cord-injured (SCI) animals and control animals with intact neuraxes. Afferent pathways from the lower urinary tract were activated either by insertion of a catheter through the urethra into the urinary bladder or by catheterisation plus induction of reflex micturition contractions by intravesical saline infusion. Placement of a catheter alone elicited Fos expression in a similar number of neurones in SCI and control rats mainly in the medial dorsal horn (MDH) and dorsal commissure (DCM) in the segments L1–2 and L5–S1 with a maximum in L5. Additional saline infusion induced low-frequency, high-amplitude, rhythmic bladder contractions of long duration in the rats with intact spinal cords, whereas in SCI rats, bladder distension elicited reflex contractions at a higher frequency, smaller amplitude and shorter duration. However, the basal and mean bladder pressure, as well as the total contraction time relative to the whole recording time, was not significantly different. Distension-induced bladder contractions markedly increased Fos expression primarily in the spinal segments L5–S1 in the control rats, where the majority of bladder and urethral afferent fibres terminates. Fos-positive cells were located in the MDH, lateral dorsal horn (LDH), DCM and the lateral aspect of laminae V–VII. Compared to controls, Fos expression after spinal cord injury (SCI) occurred in a significantly greater number of neurones throughout the segments L3–S1 following induction of bladder reflexes. The greatest proportional increase in the number of Fos-positive cells occurred in L3–5 which normally receive only little afferent input from the urinary bladder. Cell numbers predominantly increased in the LDH and lateral lamina V–VII. The data are consistent with the concept of a neuroplastic reorganisation of spinal pathways after SCI. Unmasking of silent synapses or formation of new connections by afferent axonal sprouting caudal to the lesion, as evident from the increased numbers of cells expressing Fos after bladder distension, could be factors underlying the emergence of reflexogenic micturition in chronic SCI rats. Accepted: 27 May 1999     

Effect of the NK-1 receptor antagonist GR 82,334 on reflexly-induced bladder contractions.

The effect of intrathecal administration of the novel tachykinin NK-1 receptor antagonist GR 82,334 has been tested in three reflexes which excite urinary bladder motility. GR 82,334 at 1 but not at 0.1 nmol/rat blocked the chemonociceptive micturition reflex induced by the topical application of capsaicin (4 micrograms/50 microliters) onto the urinary bladder. At the same dose proven effective in the chemonociceptive reflex, GR 82,334 did not affect either micturition reflex induced by bladder filling or the urinary bladder contraction induced by perineal pinching. These results suggest that, in urethane-anesthetized rats, specific stimuli applied in the periphery activate NK-1 receptors at spinal cord level facilitating urinary bladder reflex contractions.     

Kinin B1 receptor-mediated motor responses in normal or inflamed rat urinary bladder in vivo

The rat urinary bladder is one of the few in vivo preparations in which kinin B1 receptor-mediated contractile responses have been described, but the nature (local or reflex) of these responses has not been characterized. We have investigated the motor effects of i.v. or topical (onto the bladder serosa) administration of the selective kinin B1 receptor agonist [des-Arg9]-bradykinin ([des-Arg9]-BK) in the normal or inflamed (cyclophosphamide-induced) urinary bladder in urethane-anaesthetized rats. In both normal and inflamed bladders [des-Arg9]-BK produced a tonic contraction of low amplitude (< 15 mmHg) with phasic contractions of high amplitude (> or = 15 mmHg) superimposed (micturition reflex contractions). In inflamed bladders, the response to [des-Arg9]-BK was more prominent than in controls. Similar observations were made after the topical administration of [des-Arg9]-BK. In order to evaluate any time-dependency in the expression of B1 receptor-mediated bladder responses, [des-Arg9]-BK was administered in separate groups of control animals at 30 and 240 min after the completion of surgical procedures required for set-up of the preparation: no bladder contraction was detected at 30 min whereas both local and reflex contractions could be elicited by [des-Arg9]-BK at 240 min after the set up. In ganglionectomized rats, the response to [des-Arg9]-BK or the selective tachykinin NK2 receptor agonist [betaAla8]NKA(4-10) was evaluated at 30 and 240 min after the set up in inflamed or in control animals. The response to [des-Arg9]-BK was greater after inflammation although a time-dependent increase was evident in both groups; in contrast, the response to [betaAla8]NKA(4-10) was similar in both groups and remained constant over the observation period. After induction of inflammation, the tonic contraction induced by [des-Arg9]-BK in ganglionectomized rats was dose-dependently reduced by the kinin B1 receptor antagonist [desArg10]Hoe 140. The contractile response (number of micturition reflex contractions) induced by [des-Arg9]-BK in normal rats with intact pelvic nerves at 240 min from the set up was not changed after the administration of the selective B2 receptor antagonist Hoe 140. These results indicate that stimulation of bladder kinin B1 receptors evokes a local, tonic-type contraction with reflex contractions superimposed in both normal and inflamed bladders, but in the latter situation the motor responses are magnified.     

Role of pudendal afferents in voiding efficiency in the rat

The reciprocal activities of the bladder and external urethral sphincter (EUS) are coordinated by descending projections from the pontine micturition center but are subjected to modulation by peripheral afferent inputs. Transection of the somatic pudendal nerve innervating the striated EUS decreases voiding efficiency and increases residual urine in the rat. The reduction in voiding efficiency was attributed to the lack of phasic bursting activity of the EUS following denervation. However, transection of the pudendal nerve also eliminates somatic sensory feedback that may play a role in voiding. We hypothesized that feedback from pudendal afferents is required for efficient voiding and that the loss of pudendal sensory activity contributes to the observed reduction in voiding efficiency following pudendal nerve transection. Quantitative cystometry in urethane anesthetized female rats following selective transection of pudendal nerve branches, following chemical modulation of urethral afferent activity, and following neuromuscular blockade revealed that pudendal nerve afferents contributed to efficient voiding. Sensory feedback augmented bladder contraction amplitude and duration, thereby increasing the driving force for urine expulsion. Second, sensory feedback was necessary to pattern appropriately the EUS activity into alternating bursts and quiescence during the bladder contraction. These findings demonstrate that the loss of pudendal sensory activity contributes to the reduction in voiding efficiency observed following pudendal nerve transection, and illustrate the importance of urethral sensory feedback in regulating bladder function.     

TRPA1 receptor modulation attenuates bladder overactivity induced by spinal cord injury

The ankyrin-repeat transient receptor potential 1 (TRPA1) has been implicated in pathological conditions of the bladder, but its role in overactive bladder (OAB) following spinal cord injury (SCI) remains unknown. In this study, using a rat SCI model, we assessed the relevance of TRPA1 in OAB induced by SCI. SCI resulted in tissue damage, inflammation, and changes in bladder contractility and in voiding behavior. Moreover, SCI caused upregulation of TRPA1 protein and mRNA levels, in bladder and in dorsal root ganglion (DRG; L6-S1), but not in corresponding segment of spinal cord. Alteration in bladder contractility following SCI was evidenced by enhancement in cinnamaldehyde-, capsaicin-, or carbachol-induced bladder contraction as well as in its spontaneous phasic activity. Of relevance to voiding behavior, SCI induced increase in the number of nonvoiding contractions (NVCs), an important parameter associated with the OAB etiology, besides alterations in other urodynamic parameters. HC-030031 (TRPA1 antagonist) treatment decreased the number and the amplitude of NVCs while the TRPA1 antisense oligodeoxynucleotide (AS-ODN) treatment normalized the spontaneous phasic activity, decreased the cinnamaldehyde-induced bladder contraction and the number of NVCs in SCI rats. In addition, the cinnamaldehyde-induced bladder contraction was reduced by exposure of the bladder preparations to HC-030031. The efficacy of TRPA1 AS-ODN treatment was confirmed by means of the reduction of TRPA1 expression in the DRG, in the corresponding segment of the spinal cord and in the bladder, specifically in detrusor muscle. The present data show that the TRPA1 activation and upregulation seem to exert an important role in OAB following SCI.     

Neuronal locus and cellular signaling for stimulation of ileal giant migrating and phasic contractions

We investigated the neuronal locus, the role of PKC activation, and utilization of extracellular Ca(2+) and intracellular Ca(2+) release in smooth muscle cells for the generation of giant migrating contractions (GMCs) and rhythmic phasic contractions (RPCs) in intact normal and inflamed canine ileum. Calcitonin gene-related peptide (CGRP), administered close intra-arterially, stimulated GMCs at higher doses and RPCs at smaller doses. These effects were blocked by prior close intra-arterial infusions of CGRP(8-37), atropine, hexamethonium, and TTX but not by tachykinin, serotonin, and histaminergic receptor subtype antagonists. Both types of contractions were blocked by verapamil in normal and inflamed ileums. Dantrolene and ruthenium red blocked only the RPCs in normal ileum but blocked both GMCs and RPCs in the inflamed ileum. PKC inhibition by chelerythrine blocked GMCs only in inflamed ileum but blocked RPCs in both normal and inflamed ileums. The inhibition of phospholipase C by neomycin blocked both RPCs and GMCs in normal and inflamed ileums. In conclusion, acetylcholine is the common neurotransmitter for the stimulation of both GMCs and RPCs, but the signaling cascades for their stimulation are partially divergent, and they differ also in the normal and inflamed states.     

Analysis of the afferent limb of the vesicovascular reflex using neurotoxins, resiniferatoxin and capsaicin

The afferent limb of the vesicovascular reflex (VV-R) evoked by distension or contraction of the urinary bladder (UB) was studied in urethane-anesthetized female rats by examining the changes in VV-R after administration of C-fiber afferent neurotoxins [capsaicin and resiniferatoxin (RTX)]. Systemic arterial blood pressure increased parallel (5.1 to 53.7 mmHg) with graded increases in UB pressure (20 to 80 cm H(2)O) or during UB contractions. The arterial pressor response to UB distension was significantly reduced (60-85%) by acute or chronic (4 days earlier) intravesical administration of RTX (100-1,000 nM) or by capsaicin (125 mg/kg sc) pretreatment (4 days earlier). Chronic neurotoxin treatments also increased the volume threshold (>100%) for eliciting micturition in anesthetized rats but did not change voiding pressure. Acute RTX treatment (10-50 nM) did not alter the arterial pressor response during reflex UB contractions, whereas higher concentrations of RTX (100-1,000 nM) blocked reflex bladder contractions. It is concluded that VV-R is triggered primarily by distension- and contraction-sensitive C-fiber afferents located, respectively, near the luminal surface and deeper in the muscle layers of the bladder.     

Gentle Mechanical Skin Stimulation Inhibits Micturition Contractions via the Spinal Opioidergic System and by Decreasing Both Ascending and Descending Transmissions of the Micturition Reflex in the Spinal Cord

Recently, we found that gentle mechanical skin stimulation inhibits the micturition reflex in anesthetized rats. However, the central mechanisms underlying this inhibition have not been determined. This study aimed to clarify the central neural mechanisms underlying this inhibitory effect. In urethane-anesthetized rats, cutaneous stimuli were applied for 1 min to the skin of the perineum using an elastic polymer roller with a smooth, soft surface. Inhibition of rhythmic micturition contractions by perineal stimulation was abolished by naloxone, an antagonist of opioidergic receptors, administered into the intrathecal space of the lumbosacral spinal cord at doses of 2–20 μg but was not affected by the same doses of naloxone administered into the subarachnoid space of the cisterna magna. Next, we examined whether perineal rolling stimulation inhibited the descending and ascending limbs of the micturition reflex. Perineal rolling stimulation inhibited bladder contractions induced by electrical stimulation of the pontine micturition center (PMC) or the descending tract of the micturition reflex pathway. It also inhibited the bladder distension-induced increase in the blood flow of the dorsal cord at L5–S1, reflecting the neural activity of this area, as well as pelvic afferent-evoked field potentials in the dorsal commissure at the lumbosacral level; these areas contain long ascending neurons to the PMC. Neuronal activities in this center were also inhibited by the rolling stimulation. These results suggest that the perineal rolling stimulation activates the spinal opioidergic system and inhibits both ascending and descending transmissions of the micturition reflex pathway in the spinal cord. These inhibitions would lead to the shutting down of positive feedback between the bladder and the PMC, resulting in inhibition of the micturition reflex. Based on the central neural mechanisms we show here, gentle perineal stimulation may be applicable to several different types of overactive bladder.     

Activation and inhibition of the micturition reflex by penile afferents in the cat

Coordination of the urinary bladder and the external urethral sphincter is controlled by descending projections from the pons and is also subject to modulation by segmental afferents. We quantified the effects on the micturition reflex of sensory inputs from genital afferents traveling in the penile component of the somatic pudendal nerve by electrical stimulation of the dorsal nerve of the penis (DNP) in alpha-chloralose anesthetized male cats. Depending on the frequency of stimulation (range, 1-40 Hz), activation of penile afferents either inhibited contractions of the bladder and promoted urine storage or activated the bladder and produced micturition. Stimulation of the DNP at 5-10 Hz inhibited distension-evoked contractions and increased the maximum bladder capacity before incontinence. Conversely, stimulation at 33 and 40 Hz augmented distension-evoked contractions. When the bladder was filled above a threshold volume (70% of the volume necessary for distension-evoked contractions), stimulation at 20-40 Hz activated de novo the micturition reflex and elicited detrusor contractions that increased voiding efficiency compared with distension-evoked voiding. Electrical stimulation of the DNP with a cuff electrode or percutaneous wire electrode produced similar results. The ability to evoke detrusor contractions by activation of the DNP was preserved following acute spinal cord transection. These results demonstrate a clear role of genital afferents in modulating the micturition reflex and suggest the DNP as a potential target for functional restoration of bladder control using electrical stimulation.     

Nociceptin and the micturition reflex

The i.v. administration of nociceptin (10-100 nmol/kg) inhibits the micturition reflex in a naloxone-resistant manner. The effects induced by i.v. nociceptin were not observed in capsaicin-pretreated animals indicating that i.v. nociceptin inhibits the micturition reflex by inhibiting afferent discharge from capsaicin-sensitive nerves. Supporting this interpretation, nociceptin also inhibited the reflex but not the local bladder contraction induced by topical capsaicin and protects this reflex (but not the local contraction) by desensitization. Intrathecal nociceptin (10 nmol/rat) produces urodynamic modifications similar to those induced by the i.v. administration. Intracerebroventricular (i.c.v.) administration of nociceptin (0.3-1 nmol/rat) also inhibited the micturition reflex in a naloxone-resistant manner suggesting a direct effect on supraspinal sites controlling the micturition. Beyond the inhibitory effects exerted by nociceptin on the micturition reflex, a peripheral excitatory effect mediated by capsaicin-sensitive fibers was also detected. The application of nociceptin (5-50 nmol/rat) onto the bladder serosa when the intravesical volume was subthreshold for the triggering of the micturition reflex, activated the reflex in a dose-dependent manner; the same treatment produced a biphasic effect on the ongoing reflex. In addition to the triggering of micturition reflex, topical nociceptin evokes a local tonic-type contraction that was abolished by the coadministration of tachykinin NK(1) and NK(2) receptor antagonists. Altogether these results indicate that ORL(1) receptors are present at several sites for the integration of the micturition reflex, and that their activation may produce both excitatory or inhibitory effects, depending on the route of administration and the experimental conditions.     

Neurochemical plasticity of nitric oxide synthase isoforms in neurogenic detrusor overactivity after spinal cord injury

Nitric oxide (NO) participates in the neural pathways controlling the lower urinary tract (LUT). Expression of NO synthase (NOS) can be upregulated after spinal cord injury (SCI), and altered NOS activity may participate in resulting LUT dysfunction. To investigate distribution of NOS-immunoreactivity (NOS-IR) in neurons of rats following SCI and the possible effects of NOS inhibitors. Expression of neuronal and inducible NOS-IR in lumbosacral spinal cord was assessed in rats. Cystometry was performed to examine effects of intrathecal injection of NOS inhibitor. There was increased expression of neuronal NOS-IR after trauma. Maximum bladder capacity was increased by neuronal NOS (nNOS) inhibitors. Upregulation of nNOS may facilitate emergence of the spinal micturition reflex following SCI; nNOS inhibitor suppressed SCI-induced urinary incontinence by increasing bladder capacity. Our results indicate manipulation of NO production could help treat LUT dysfunction after SCI.     

Urinary bladder function in conscious rat pups: a developmental study

Cystometric studies of bladder function in anesthetized neonatal rats have suggested specific changes in urodynamic parameters that coincide with the development of a mature bladder-to-bladder micturition reflex. Here, we used a conscious cystometry model that avoids the potentially confounding effects of anesthesia to characterize voiding patterns and urodynamic parameters during early postnatal development in healthy rat pups. Cystometry was performed on postnatal day (P)0, 3, 7, 14, and 21 rats with continuous intravesical instillation of NaCl via a bladder catheter. Micturition cycles were analyzed with respect to voiding pattern, nonvoiding contractions, infused volume, and basal, filling, threshold, and micturition pressures. Reproducible micturition patterns were obtained from all age groups. The time from stimulation to contraction was significantly longer (P ≤ 0.001) in ≤1-wk-old rats (～10 s) than that in older rats (～3 s). An interrupted voiding pattern was observed in ≤10-day-old subgroups. Micturition pressure progressively increased with age (from 21.77 ± 1.92 cmH(2)O at P0 to 35.47 ± 1.28 cmH(2)O at P21, P ≤ 0.001), as did bladder capacity. Nonvoiding contractions were prominent in the P3 age group (amplitude: 4.6 ± 1.3 cmH(2)O, frequency: ～4.0 events/100 s). At P7, the pattern of spontaneous contractions became altered, acquiring a volume-related character that persisted in a less prominent manner through P21. Bladder compliance increased with age, i.e., maturation. In conclusion, conscious cystometry in rat pups resulted in reproducible micturition cycles that yielded consistent data. Our results revealed immature voiding and prolonged micturition contractions during the first 10 neonatal days and provide evidence for age-related changes in urodynamic parameters.     

Exposure to extremely low-frequency magnetic field restores spinal cord injury-induced tonic pain and its related neurotransmitter concentration in the brain

Spinal cord injury (SCI) is unequivocally reported to produce hyperalgesia to phasic stimuli, while both hyper- and hypoalgesia to tonic stimuli. The former is spinally mediated and the latter centrally. Besides, its management is unsatisfactory. We report the effect of magnetic field (MF; 17.96 μT, 50 Hz) on tonic pain behavior and related neurotransmitters in the brain of complete thoracic (T13) SCI rats at week 8. Adult male Wistar rats were divided into Sham, SCI and SCI+MF groups. Formalin-pain behavior was compared utilizing 5 min block pain rating (PR), 60 min session-PR, time spent in various categories of increasing pain (T0–T3) and flinch incidences. Serotonin (5-HT), dopamine (DA), norepinepherine (NE), gamma-aminobutyric acid (GABA), glutamate and glycine were estimated in brain tissue by liquid chromatography–mass spectrometry. Session-PR, block-PR and number of flinches were significantly lower, while time spent in categories 0–1 was higher in the SCI versus Sham group. These parameters were comparable in the SCI+MF versus Sham group. 5-HT concentration in cortex, remaining forebrain areas and brain stem (BS), was lower while GABA and NE were higher in BS of SCI, which were comparable with Sham in the SCI+MF group. The concentration of DA, glutamate and glycine was comparable amongst the groups. The data indicate significant hypoalgesia in formalin pain while increased in GABA, NE and decreased in 5-HT post-SCI, which were restored in the SCI+MF group. We suggest beneficial effect of chronic (2 h/day × 8 weeks) exposure to MF (50 Hz, 17.96 μT) on tonic pain that is mediated by 5-HT, GABA and NE in complete SCI rats.     

Effect of naftopidil,an alpha1D/A-adrenoceptor antagonist,on the urinary bladder in rats with spinal cord injury

AimsAlpha_1D-adrenoceptors (α_1D-ARs) located in the spinal cord are involved in the control of lower urinary tract function. In order to clarify the effect of α_1D-ARs on storage function in the spinal cord, we examined the effect of oral administration and intrathecal injection of the α_1D/A-AR antagonist, naftopidil, on bladder activity, as well as the effect of naftopidil on bladder wall histology, in female rats with spinal cord injury (SCI).Main methodsAdult female Sprague–Dawley rats with Th9–10 spinal cord transection were used. In SCI rats with or without 5 mg/day of naftopidil for 4 weeks, bladder activity was examined via continuous cystometry. In other SCI rats, bladder activity was examined before and after intrathecal injection of naftopidil. In addition, bladder wall histology was compared between SCI rats with or without oral administration of naftopidil for 4 weeks.Key findingsOral administration of naftopidil decreased the number of non-voiding contractions (NVCs). Intrathecal injection of naftopidil prolonged the interval between voiding contractions, decreased the maximum voiding contraction pressure and the number of NVCs, and increased bladder capacity without affecting the residual urine volume. Oral administration of naftopidil also decreased bladder wall fibrosis.SignificanceThe α_1D/A-AR antagonist naftopidil might act on the bladder and spinal cord to improve detrusor hyperreflexia in the storage state in SCI female rats. Naftopidil also suppressed bladder wall fibrosis, suggesting that it may be effective for the treatment of neurogenic lower urinary tract dysfunction after SCI.     

A spinal site mediates opiate analgesia in frogs

The application of acetic acid to the hind leg of a frog will induce a spinally mediated wiping reflex only if the acetic acid concentration is above a certain threshold. By using this reflex as the basis of a test for nociception, we show that morphine sulfate is a potent analgesic in the frog when injected into the lumbar area of the spinal cord. Significant analgesia is induced within 5 min after injection of as little as 0.0316 μg of morphine sulfate. Low doses of morphine sulfate (0.0316 or 0.1 μg) induce analgesia which dissipates within 1 h while for higher doses (0.316, 1.0 or 3.16 μg) the analgesia persists for at least 3 h. The analgesic effect of 0.316 μg of morphine sulfate is completely blocked by naloxone HCl at either 0.158 or 0.316 μg. Animals receiving naloxone alone (0.316 μg) appear to be slightly hyperalgesic compared to saline injected controls but this effect is not significant.     

Receptor activated bladder and spinal ATP release in neurally intact and chronic spinal cord injured rats

Neurally intact (NI) rats and chronic spinal cord injured (SCI) rats were studied to determine how activation of mechanosensory or cholinergic receptors in the bladder urothelium evokes ATP release from afferent terminals in the bladder as well as in the spinal cord. Spinal cord transection was performed at the T(9)-T(10) level 2-3 weeks prior to the experiment and a microdialysis fiber was inserted in the L(6)-S(1) lumbosacral spinal cord one day before the experiments. Mechanically evoked (i.e. 10 cm/W bladder pressure) ATP release into the bladder lumen was approximately 6.5-fold higher in SCI compared to NI rats (p<0.05). Intravesical carbachol (CCh) induced a significantly greater release of ATP in the bladder from SCI as compared to NI rats (3424.32+/-1255.57 pmol/ml versus 613.74+/-470.44 pmol/ml, respectively, p<0.05). However, ATP release in NI or SCI rats to intravesical CCh was not affected by the muscarinic antagonist atropine (Atr). Spinal release of ATP to bladder stimulation with 10 cm/W pressure was five-fold higher in SCI compared to NI rats (p<0.05). CCh also induced a significantly greater release of spinal ATP in SCI rats compared to controls (4.3+/-0.9 pmol versus 0.90+/-0.15 pmol, p<0.05). Surprisingly, the percent inhibitory effect of Atr on CCh-induced ATP release was less pronounced in SCI as compared to NI rats (49% versus 89%, respectively). SCI induces a dramatic increase in intravesical pressure and cholinergic receptor evoked bladder and spinal ATP release. Muscarinic receptors do not mediate intravesical CCh-induced ATP release into the bladder lumen in NI or SCI rats. In NI rats sensory muscarinic receptors are the predominant mechanism by which CCh induces ATP release from primary afferents within the lumbosacral spinal cord. Following SCI, however, nicotinic or purinergic receptor mechanisms become active, as evidenced by the fact that Atr was only partially effective in inhibiting CCh-induced spinal ATP release.     

Effect of enkephalin on the micturition cycle of the cat

The effect of the synthetic opiate [D-Ala2, Me-Phe4]-leu-enkephalin ( DAMLE ) on the micturition cycle of the cat was studied. In vivo assays were performed with young male cats under two different conditions: 1) decerebrated cats (D-cats), with an intercollicular transection of the brainstem, and 2) spinal cats (S-cats), with a spinal transection between C5-C6. In vitro studies were carried out on bladder strips taken from adult male cats. The D-cats showed two types of voiding patterns: the first type (I) was characterized by a smooth wave of pressure and an incomplete emptying of the bladder; the second type (II) began like the type I, but ended with a series of small contractions accompanied by small jets of liquid, resulting in the complete emptying of the bladder. DAMLE inhibited vesical contractions and completely inhibited voiding in D-cats at doses equal or superior to 250 micrograms/kg i.v.; no effect was noted with lower doses. Vesical contractions were hardly affected in S-cats, even at high doses (greater than 350 micrograms/kg i.v.). DAMLE did not affect electrically induced contractions of isolated bladder strips. Naloxone not only antagonized the inhibitory effects of DAMLE , but also induced per se a contraction of the bladder. These results indicate that enkephalinergic neurons are involved in the central neural circuitry of the micturition cycle in the cat, with an inhibitory effect at the level of either the ascending spinal pathways or the pontine Barrington 's center.     

Substance P in the baroreceptor reflex: 25 years

Twenty-five years ago, very little was known about chemical communication in the afferent limb of the baroreceptor reflex arc. Subsequently, considerable anatomic and functional data exist to support a role for the tachykinin, substance P (SP), as a neuromodulator or neurotransmitter in baroreceptor afferent neurons. Substance P is synthesized and released from baroreceptor afferent neurons, and excitatory SP (NK1) receptors are activated by baroreceptive input to second-order neurons. SP appears to play a role in modulating the gain of the baroreceptor reflex. However, questions remain about the specific role and significance of SP in mediating baroreceptor information to the central nervous system (CNS), the nature of its interaction with glutaminergic transmission, the relevance of colocalized agents, and complex effects that may result from mediation of non-baroreceptive signals to the CNS.     

Effects of a new analgesic agent, D57, on sodium currents in afferent neurons of the rat ganglia

We studied the effects of a new analgesic agent, D57 (a pyrrolimidazol derivative), on sodium currents in isolated afferent neurons of the trigeminal and spinal ganglia of rats. It is demonstrated that D57 exerts both tonic and phasic effects on sodium currents. In the neurons of a nociceptive system influenced by D57, phasic blocking provides suppression of more than 50% of the currents that persisted after the development of tonic blocking. At the same time, in the neurons supposedly belonging to other afferent systems, the contribution of phasic blocking was only about 20%. We hypothesize that high intensity of phasic blocking of sodium ion currents in the neurons of the nociceptive system represents a factor responsible for analgesic properties of D57.