Biomedical subjects

W C De Groat

Publications and source records attributed to W C De Groat.

At least 19 recordsLinked to original sources

PubMed2003

Role of protein kinase C in central muscarinic inhibitory mechanisms regulating voiding in rats.

To evaluate the role of protein kinase C in central muscarinic mechanisms regulating voiding, cystometry was performed in conscious rats. Oxotremorine methiodide, a muscarinic agonist was injected i.c.v. in a dose (0.1 microg/rat) shown previously to alter voiding function. Oxotremorine methiodide was also tested after i.c.v. injection of chelerythrine chloride (a protein kinase C inhibitor, 2 microg/rat) or 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H-7, a protein kinase inhibitor, 5 nmol/rat). In untreated rats, oxotremorine methiodide elicited a bimodal response consisting of an initial increase in bladder capacity, maximal voiding pressure, pressure threshold and post voiding intravesical pressure, but reduced voiding efficiency and bladder compliance. The second response consisted of a decrease in bladder capacity and bladder compliance, increases in maximal voiding pressure and post voiding intravesical pressure, but no change in pressure threshold or voiding efficiency. However, approximately 20 min after pre-treatment with chelerythrine chloride or H-7 in doses that did not alter voiding function, oxotremorine methiodide decreased bladder capacity, increased maximal voiding pressure, but did not change pressure threshold or voiding efficiency. These results indicate that inhibitory and facilitatory muscarinic mechanisms in the brain that control voiding function involve different second messenger systems. Inhibitory mechanisms which are blocked by chelerythrine chloride or H-7 must involve protein kinase C and normally be inactive because the protein kinase inhibitors alone did not alter voiding. On the other hand, facilitatory muscarinic mechanisms which previous studies showed were tonically active are not mediated by chelerythrine chloride or H-7 sensitive signaling pathways.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗

PubMed2002

Altered urinary bladder function in mice lacking the vanilloid receptor TRPV1.

In the urinary bladder, the capsaicin-gated ion channel TRPV1 is expressed both within afferent nerve terminals and within the epithelial cells that line the bladder lumen. To determine the significance of this expression pattern, we analyzed bladder function in mice lacking TRPV1. Compared with wild-type littermates, trpv1(-/-) mice had a higher frequency of low-amplitude, non-voiding bladder contractions. This alteration was accompanied by reductions in both spinal cord signaling and reflex voiding during bladder filling (under anesthesia). In vitro, stretch-evoked ATP release and membrane capacitance changes were diminished in bladders excised from trpv1(-/-) mice, as was hypoosmolality-evoked ATP release from cultured trpv1(-/-) urothelial cells. These findings indicate that TRPV1 participates in normal bladder function and is essential for normal mechanically evoked purinergic signaling by the urothelium.

Acetic Acid↗

PubMed2002

ATP is released from guinea pig ureter epithelium on distension.

Distension of the perfused guinea pig ureter at pressures from 20 to 700 cmH(2)O increased the amount of ATP released from the epithelium in a pressure-dependent manner. During basal perfusion (40 microl/min), the perfusate contained 10 pmol/ml ATP; this increased 10- to 50-fold at various distending pressures. ATP was released from epithelial cells during distension as mechanical removal of the urothelium blocked release. No lactate dehydrogenase was detected in the perfusate, and scanning electron microscopy confirmed an intact urothelium after distension. ATP was not released due to the activation of stretch-activated channels, as gadolinium (10 microM) failed to affect ATP release. Glibenclamide (10 microM), known to inhibit two members of the ATP-binding cassette (ABC) protein family, did not affect ATP release after distension; nor did verapamil (10 microM). In contrast, both monensin (100 microM) and brefeldin A (10 microM), which interfere with vesicular formation or trafficking, inhibited distension-evoked ATP release, which was Ca(2+)-dependent. This suggests that ATP release from the ureter epithelium might be mediated by vesicular exocytosis. The role of ATP released by distension of hollow visceral organs is discussed in relation to the concept of purinergic mechanosensory transductions, with special reference to nociception and the activation of P2X(3) receptors on the subepithelial sensory nerves.

Adenosine Triphosphate↗

PubMed2001

Facilitation of transmitter release in the urinary bladders of neonatal and adult rats via alpha1-adrenoceptors.

Age-dependent changes in the effects of the alpha1-adrenoceptor agonist, phenylephrine were investigated on neurally evoked contractile responses and basal tone in smooth muscle strips from rat urinary bladder. Phenylephrine facilitated the neurogenic contractions in both neonatal and 7-month-old adult rats. However, phenylephrine increased the basal tone in adult but not neonatal rats. In adult rats, phenylephrine-induced facilitation of neurally evoked contractions occurred before and after the block of cholinergic contractions with 1 microM atropine. In adult rats, the phenylephrine facilitation was reduced at stimulation parameters (20 Hz, 80 shocks and maximal voltage) which activated muscarinic receptor mediated facilitation of acetylcholine release. The results indicate that pre-synaptic alpha1-adrenoceptors facilitate the release of both acetylcholine and the non-cholinergic non-adrenergic transmitter. In summary, alpha1-adrenoceptor-mediated facilitation is less expressed when muscarinic M1 receptor mediated facilitation is functioning; pre-junctional alpha1-adrenoceptors are present in the bladder of both neonatal and adult rats, whereas post-junctional alpha1-adrenoceptors are expressed only in older adult rats.

Acetylcholine↗

PubMed2001

Effects of WAY100635, a selective 5-HT1A-receptor antagonist on the micturition-reflex pathway in the rat.

5-Hydroxytryptamine (5-HT) receptors in the central nervous system have been implicated in the control of micturition. The present study was undertaken to evaluate the effects of a selective 5-HT1A-receptor antagonist [N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl)cyclohexanecarboxamide trihydrochloride (WAY100635)] on the micturition-reflex pathway in urethane-anesthetized female Wistar rats. Rhythmic isovolumetric bladder contractions evoked by bladder distension were abolished by 0.3- to 3-mg/kg iv or 30- to 100-microg intrathecal (it) administration of WAY100635 in a dose-dependent manner for periods of 3-15 min. Intrathecal injection of WAY100635 was effective only if injected at the L6-S1 spinal cord level, but not at the thoracic or cervical cord levels. WAY100635 (30-100 microg it) significantly reduced the amplitude of bladder contractions evoked by electrical stimulation of the pontine micturition center. However, the field potentials in the rostral pons evoked by electrical stimulation of pelvic nerve were not affected by intrathecal or intravenous injection of WAY100635. These results suggest that 5-HT1A receptors at the L6-S1 level of the spinal cord have an important role in the tonic control of the descending limb of the micturition-reflex pathway in the rat.

Animals↗

PubMed2001

Role of spinal alpha1-adrenoceptor subtypes in the bladder reflex in anesthetized rats.

The contribution of different subtypes of alpha1-adrenoceptors in the lumbosacral spinal cord to the control of the urinary bladder was examined in urethane-anesthetized rats. Bladder pressure was recorded via a transurethral catheter under isovolumetric conditions. Drugs were administered intrathecally at the L6-S1 segmental level of spinal cord. RS-100329 (an alpha1A-antagonist) in doses of 25, 50, and 100 nmol significantly decreased bladder-contraction amplitude by 38%, 52%, and 95%, respectively, whereas (+)-cyclazosin (an alpha1B-antagonist) significantly decreased bladder-contraction amplitude (48% reduction) only in a 50-nmol but not a 100-nmol dose. Fifty nanomoles of RS-100329 and (+)-cyclazosin increased bladder-contraction frequency by 54% and 44%, respectively. BMY7378 (an alpha1D-antagonist), in doses of 25, 50, and 100 nmol, did not change bladder activity. These studies suggest that reflex-bladder activity is modulated by two types of spinal alpha1-adrenergic mechanisms: 1) alpha1A- or alpha1B-inhibitory control of the frequency of voiding reflexes presumably mediated by an alteration in the processing of bladder afferent input and 2) alpha(1A)-facilitatory modulation of the descending efferent limb of the micturition-reflex pathway. Spinal alpha1D-adrenoceptors do not appear to have a significant role at either site.

Anesthesia, General↗

PubMed1999

Effects of N-methyl-D-aspartate (dizocilpine) and alpha-amino-3-hydroxy-4-isoxazolepropionate (LY215490) receptor antagonists on the voiding reflex induced by perineal stimulation in the neonatal rat.

The present study was undertaken to examine the role of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate and N-methyl-D-aspartate glutamate receptors in the regulation of voiding reflexes induced by perineal stimulation in the neonatal rat. Four-, six- and 10-day-old awake rats were used in the experiments and perineal stimulation was applied using the tip of a 1-ml syringe to evoke voiding. Voided volume and residual volume were measured. In 10-day-old rats, LY215490 (3-10 mg/kg, i.p.), a competitive alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate receptor antagonist, significantly inhibited reflex voiding, increasing the residual volume 34-53-fold. A 3 mg/kg dose decreased the urine release by 55%, whereas 10 mg/kg totally suppressed the voiding reflex induced by the perineal stimulation. LY215490 (10 mg/kg, i.p.) produced similar effects in four- and six-day-old rats. Dizocilpine (1-3 mg/kg, i.p.), a non-competitive N-methyl-D-aspartate receptor antagonist, also significantly decreased the urine release (62-82%) and increased residual volume (180-230-fold). Combined administration of LY215490 (1 mg/kg, i.p.) and dizocilpine (0.3 mg/kg, i.p.) to 10-day-old rats, in doses that individually had no effect on perineal stimulation-evoked voiding, depressed voided volume by 65%. These results indicate that, in neonatal rats, glutamatergic transmission in the spinal cord has an essential role in reflex micturition induced by perineal stimulation, and that facilitatory interactions between alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate and N-methyl-D-aspartate glutamatergic mechanisms are important for voiding, as noted previously in adult rats.

Aging↗

PubMed1999

Urethral afferent nerve activity affects the micturition reflex; implication for the relationship between stress incontinence and detrusor instability.

PURPOSE: A causative relationship between stress urinary incontinence (SUI) and detrusor instability has been suspected but never proven. Many women with mixed incontinence have resolution of detrusor instability after surgical correction of SUI. We sought experimental support that stimulation of urethral afferent nerves can induce or change reflex detrusor contractions. MATERIALS AND METHODS: Urethral perfusion pressure and isovolumetric bladder pressure were measured with catheters inserted through the bladder dome in urethane anesthetized female S.D. rats (250 to 300 grams; n = 12). The catheter assembly was seated securely in the bladder neck to block passage of fluid between the bladder and urethra without affecting the nerve supply to the organs. The external urethra was not catheterized. Responses were examined in the control state at a urethral saline perfusion speed of 0.075 ml. per minute. Intraurethral drugs were administered following blockade of striated sphincter activity with intravenous alpha-bungarotoxin (0.1 mg./kg.). RESULTS: Stopping the urethral saline infusion caused a significant decrease in micturition frequency in approximately 50% of the animals studied (n = 12). Intraurethral lidocaine (1%) infused at 0.075 ml. per minute caused a slight decrease in urethral perfusion pressure but no change in detrusor contraction amplitude. However, intraurethral lidocaine caused a significant (45%) decrease in the bladder contraction frequency (n = 5). The micturition frequency returned to baseline 30 minutes after stopping lidocaine infusion. Intraurethral infusion of nitric oxide (NO) donors (S-nitroso-N-acetylpenicillamine [SNAP] (2 mM) or nitroprusside (1 mM) immediately decreased urethral perfusion pressure by 30 to 37% (n = 5). A 45 to 75% decrease (n = 5) in bladder contraction frequency was also seen, which was similar to that observed following lidocaine. Neither NO donor changed the amplitude of bladder contractions. CONCLUSIONS: These results indicate that in the anesthetized rat activation of urethral afferents by urethral perfusion can modulate the micturition reflex. Thus in patients with stress urinary incontinence, leakage of urine into the proximal urethra may stimulate urethral afferents and facilitate voiding reflexes. This implies that stress incontinence can induce and/or increase detrusor instability. These findings have significant implications for the treatment of patients with mixed urge and stress incontinence. Correction of stress incontinence by surgery or pelvic floor exercise in patients with mixed incontinence may resolve the detrusor instability.

Anesthetics, Local↗

PubMed1998

Adrenergic- and capsaicin-evoked nitric oxide release from urothelium and afferent nerves in urinary bladder.

Nitric oxide (NO) has been implicated in the regulation of the lower urinary tract. However, the source(s) of NO production in the urinary bladder (UB) has not been determined. Accordingly, we used a porphyrinic microsensor placed on the surface of UB strips in vitro to directly measure endogenous NO production. The afferent neurotoxin, capsaicin, and the mixed alpha/beta-adrenergic agonist, norepinephrine (NE), both evoked transient (1-3 s) NO release (range 50 nM to 1.4 microM). Adrenergic-mediated release was not decreased following denervation of the UB but was abolished following selective removal of the mucosa. On the other hand, release evoked by capsaicin (range 50-900 nM) was significantly decreased after UB denervation. These data indicate that NE releases NO from UB epithelium, and capsaicin releases NO from epithelium as well as nervous tissue in the UB. In light of reports that NO may regulate epithelial integrity and function in other tissues, agonist regulation of a constitutive nitric oxide synthase activity in the UB may provide a novel mechanism for modulation of bladder and urothelial function.

Adrenergic Agonists↗

PubMed1998

Role of spinal glutamatergic transmission in the ascending limb of the micturition reflex pathway in the rat.

This study was undertaken to evaluate the role of glutamate receptors at spinal synapses on the ascending limb of the micturition reflex. In urethane-anesthetized female rats, a tungsten electrode was inserted stereotaxically into the dorsal part of the rostral pons to record field potentials which were evoked by electrical stimulation of the pelvic nerve (PLN) (1-15 V, 0.05 ms pulse duration at 100-300 Hz, 5-30 ms train duration). The effects of glutamate receptor antagonists administered intrathecally (i.t.) on the PLN-evoked field potentials in the dorsal part of the rostral brainstem were examined. PLN stimulation evoked short latency (10-22 ms) negative field potentials (85 +/- 4 microV) in a limited area of the dorsal part of the rostral pons (bregma -9.0 to -8.4, L 0.5 to 1. 5, H 4.2 to 5.4). The i.t. administration of LY215490 (0.1-30 microg), a competitive alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor antagonist, reduced the amplitude of the evoked potentials in a dose-dependent manner; 84 +/- 6%, 59 +/- 11% (P < .001), 31 +/- 10% (P < .001), 17 +/- 9% (P < .001) of control after 0.1, 1, 10, 30 microg of LY215490, respectively. The i.t. administration of MK-801 (1-100 microg), a noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist, also reduced the amplitude of the evoked potentials in a dose-dependent manner; 93 +/- 21%, 76 +/- 14%, 52 +/- 9% (P < .001), 39 +/- 9% (P < .001) of control after 1, 10, 30, 100 microg of MK-801, respectively. Combined administration of LY215490 (0.1 microg) and MK-801 (1 microg), in doses which individually did not elicit a significant effect, markedly reduced the amplitude of the evoked potentials (27 +/- 9% of control, P = . 0002). These results suggest that AMPA and NMDA glutamatergic synaptic mechanisms play a key role in the spinal processing of afferent input from the bladder and that these mechanisms function synergistically in the ascending limb of the spinobulbospinal micturition reflex pathway.

Afferent Pathways↗

PubMed1997

Reflex pathways controlling urethral striated and smooth muscle function in the male rat.

The organization of vesicourethral reflex mechanisms in the male rat was studied by monitoring intraurethral pressure and the external urethral sphincter (EUS) electromyogram. EUS striated and urethral smooth muscle activities were elicited by reflex isovolumetric bladder contractions evoked by bladder filling or electrical stimulation of nerves in the bladder wall. Evoked EUS bursting activity in normal rats was eliminated in chronic spinal rats and replaced by tonic activity. Reflex urethral smooth muscle activity mediated by an increase in urethral pressure after paralysis of the EUS with alpha-bungarotoxin occurred in normal and chronic spinal rats. The response was significantly larger in chronic spinal (21.3 +/- 3.0 cmH2O) than in normal rats (4.2 +/- 0.7 cmH2O). NG-nitro-L-arginine methyl ester (a nitric oxide synthase inhibitor, 20 mg/kg i.v.) increased the smooth muscle response in normal (5.9 +/- 1.3 cmH2O) and chronic spinal rats (6.9 +/- 1.8 cmH2O). This increase in urethral pressure was not changed by sympathetic nerve transection or prazosin (0.2-0.3 mg/kg i.v.) but was abolished by hexamethonium and reduced 74-89% by atropine. These results indicate that coordinated EUS function (bursting activity) in the male rat is dependent on supraspinal pathways and that the urethral smooth muscle response during voiding is composed of a predominant cholinergic, atropine-sensitive contraction as well as a nitric oxide-mediated relaxation. Both are mediated by activation of parasympathetic pathways and are maintained or significantly larger after spinal cord injury, indicating that they are dependent on spinal reflex pathways.

Adrenergic alpha-Antagonists↗

PubMed1996

Unitary excitatory synaptic currents in preganglionic neurons mediated by two distinct groups of interneurons in neonatal rat sacral parasympathetic nucleus.

1. Excitatory postsynaptic currents (EPSCs) in parasympathetic preganglionic neurons (PGNs) were examined by the use of the whole cell patch-clamp recording technique in slice preparations of the neonatal rat lumbosacral spinal cord. Synaptic responses were evoked in PGNs by extracellular stimulation of a neighboring interneuron. 2. Stimulation of interneurons medial to the sacral parasympathetic nucleus (SPN) elicited EPSCs or inhibitory postsynaptic currents in 58 and 11%, respectively, of PGNs. Stimulation of interneurons dorsal to the SPN evoked EPSCs in 70% of PGNs. 3. EPSCs occurred at short latency (2.1 ms) and were usually elicited in an all-or-none manner, indicating that they were monosynaptic and mediated by a single interneuron (i.e., unitary). 4. EPSCs were mediated by both non-N-methyl-D-aspartate (non-NMDA) and NMDA receptors. 5. Unitary excitatory postsynaptic potentials evoked by single stimuli did not induce action potentials in PGNs, but repetitive stimulation (> 20 Hz) of the single interneurons could evoke firing of PGNs. 2-Amino-5-phosphonovalerate, an NMDA receptor antagonist, reduced the synaptic depolarization induced in PGNs by high-frequency interneuronal impulses. 6. EPSCs mediated by dorsal interneurons were smaller in amplitude (36.3 +/- 15.7 pA, mean +/- SD) than EPSCs mediated by medial interneurons (88.4 +/- 45.7 pA). 7. Paired-pulse facilitation of EPSCs was observed in PGNs (147.2 +/- 26.2%). The degree of facilitation was higher in dorsal (174.6 +/- 10.3%) than in medial interneuronal pathways (120.9 +/- 3.6%). Within each of interneuronal pathways the degree of facilitation was independent of the magnitude of the unitary EPSC. 8. The results show that PGNs receive monosynaptic glutamatergic excitatory inputs from two distinct populations of interneurons in the dorsal and medial regions of the SPN. These two populations of interneurons are likely to have different functions in the regulation of the preganglionic outflow to the pelvic organs.

Animals↗

PubMed1996

Characterization of voltage-sensitive Na+ and K+ currents recorded from acutely dissociated pelvic ganglion neurons of the adult rat.

1. Electrophysiological properties of acutely dissociated neurons from the major pelvic ganglion (MPG) of the adult male rat were studied with whole cell patch-clamp recording techniques. The MPG neurons innervating the urinary bladder were labeled by retrograde axonal tracing methods with the use of a fluorescent dye, Fast Blue (FB) injected into the bladder wall and identified with a fluorescent microscope. 2. Passive and active membrane properties such as resting membrane potential, input resistance, duration of action potentials, thresholds for spike activation, or duration of afterhyperpolarization in unidentified MPG neurons were comparable with those of FB-labeled neurons innervating the urinary bladder. The action potential in both unidentified and bladder efferent MPG neurons was reversibly abolished by tetrodotoxin (TTX, 1 microM). The afterhyperpolarization of the TTX-sensitive action potential in both groups was reduced by application of Cd2+ (0.1 mM) and further suppressed by tetraethylammonium (TEA, 10 mM). Extracellularly applied TEA increased the duration of the action potential, and 4-aminopyridine (4-AP, 1 or 2 mM) also reduced the spike afterhyperpolarization and increased the spike duration. The duration of the action potential was decreased and the rate of spike repolarization was increased by approximately 2.5-fold with negative shift of membrane potential from -40 to -80 mV. 3. The isolated Na+ current was reversibly blocked by 1 microM TTX and had a mean peak amplitude of 127.3 pA/pF when activated from a holding potential of -70 mV in the external solution containing 100 mM Na+. The Na+ conductance reached half-maximal activation at a membrane potential of -21.5 mV with a slope factor of 4.9 mV. The steady-state inactivation of Na+ conductance occurred at membrane potentials more depolarized than -90 mV, and the half-maximal inactivation was obtained at -57.5 mV with a slope factor of 8.8 mV. 4. The fast-transient A-type K+ current (IA) was activated at membrane potentials more depolarized than -60 mV from a holding membrane potential of -100 mV, reached a peak amplitude within 10 ms after the onset of depolarizing voltage steps, and decayed within 20-30 ms at membrane potential depolarizations to +20 to +30 mV. The IA current activated by a voltage step to +20 mV from a holding potential of -100 mV averaged 102.1 pA/pF. The half-maximal activation of the IA conductance was obtained at a membrane potential of -21.2 mV with a slope factor of 9.9 mV. In steady-state inactivation of IA current, the half-maximal inactivation occurred at -76.5 mV and the slope factor was 8.0 mV. 5. The delayed K+ current was reduced by 25-35% by bath application of Cd2+ or the elimination of extracellular Ca2+ ions. The bath application of 4-AP (2 mM) suppressed the IA current by 75% and the delayed K+ current by 60%. Extracellularly applied TEA (10 mM) suppressed the delayed K+ current by 90%, but suppressed the IA current by only 16%. 6. These results indicate that bladder neurons and unidentified neurons in the MPG have similar properties including a TTX-sensitive Na+ current and three distinct types of voltage-sensitive K+ currents-IA current, Ca(2+)-activating K+ current, and delayed rectifier K+ current-that contribute to the repolarization phase of the action potential. These electrical properties of the MPG neurons resemble those of sympathetic neurons in the superior cervical and inferior mesenteric ganglia.

Action Potentials↗

PubMed1995

Interactions between NMDA and AMPA/kainate receptors in the control of micturition in the rat.

In unanesthetized decerebrate rats, GYKI 52466 (1-(4-aminophenyl)-4-methyl-7,8-methylenedioxy-5H-2,3-benzodiazepine hydrochloride), an AMPA/kainate receptor antagonist, and MK-801 (dizocilpine), an NMDA receptor antagonist, acted synergistically to depress the micturition reflex. MK-801 (1 mg/kg i.v.) and GYKI 52466 (4 mg/kg i.v.) administered separately had no or only a small depressant effect on reflex bladder contractions but markedly depressed external urethral sphincter activity. However, in MK-801-treated rats, GYKI 52466 decreased the amplitude, frequency and duration of reflex bladder contractions. These results suggest that both AMPA/kainate and NMDA glutamate receptors are important in the micturition reflex pathway and that these receptors may be activated in parallel at some site in the pathway so that excitatory transmission via only one receptor type is sufficient to mediate reflex activation of the bladder.

Animals↗

PubMed1995

Voltage-dependent potentiation of neuronal L-type calcium channels due to state-dependent phosphorylation.

Modulation of Ca2+ channels during repetitive activity in excitable cells can have an important role in altering cellular function. In mammalian parasympathetic and dorsal root ganglion neurons, L-type Ca2+ channels are potentiated by single depolarizing prepulses or trains of short high-frequency depolarizing pulses. This type of potentiation takes place regardless of whether Ca2+ or Ba2+ is the charge carrier and requires phosphorylation by a adenosine 3',5'-cyclic monophosphate (cAMP)-dependent protein kinase. The magnitude of facilitation was correlated with frequency of conditioning trains, was enhanced by 8-bromoadenosine 3',5'-cyclic monophosphate or the Sp diastereomer of adenosine 3',5'-cyclic monophosphothioate (cAMPS), and reduced by Rp-cAMPS or a peptide inhibitor of cAMP-dependent protein kinase. The N-type Ca2+ channels exhibited the opposite response to these agents. We propose that the potentiation of L-type Ca2+ channel currents in neurons is due to state-dependent phosphorylation by cAMP-dependent protein kinase (Sculptoreanu, A., T. Scheuer, and W. A. Catterall. Nature Lond. 364: 240-243, 1993; Sculptoreanu, A., E. Rotman, M. Takahashi, T. Scheuer, and W. A. Catterall. Proc. Natl. Acad. Sci. USA 90: 10135-10139, 1993.). Thus state-dependent phosphorylation in neurons may be a mechanism for the regulation of various functions including transmitter release.

Animals↗

PubMed1994

Alteration by urethane of glutamatergic control of micturition.

The i.v. administration of MK-801 (0.001-3 mg/kg), a non-competitive NMDA receptor antagonist, did not alter reflex bladder activity in unanesthetized decerebrate rat recorded during fast infusion (0.21 ml/min) cystometry or under isovolumetric conditions, but did depress reflex bladder contractions in doses between 0.1 and 3 mg/kg i.v. in the urethane-anesthetized (1.2 g/kg s.c.) intact rat during fast infusion cystometry. The ED50 and the dose to produce maximal inhibition in urethane-anesthetized intact rats were 0.25 mg/kg and 3 mg/kg i.v., respectively. During slow infusion (0.04 ml/min) cystometry, in unanesthetized decerebrate rats, MK-801 (0.1-1 mg/kg i.v. or 6-60 micrograms i.t.) decreased by 12-44% the micturition volume threshold (VT) but did not change the amplitude and duration of the bladder contractions. The administration of a larger i.t. dose (60 micrograms) of MK-801 produced no further decrease in VT but decreased the amplitude of bladder contractions by 24%. External urethral sphincter electromyogram activity was reduced or abolished by MK-801 (0.01-3 mg/kg i.v.) in both unanesthetized decerebrate and urethane-anesthetized intact rats with ED50 of 0.12 mg/kg and 0.05 mg/kg, respectively. These results indicate that NMDA receptors play an important role in both facilitatory and inhibitory central neural control of voiding function and that there is a significant interaction between urethane anesthesia and NMDA glutamatergic transmission. Thus, even though urethane anesthesia has been useful for studying the physiological characteristics of the micturition reflex, it seems inappropriate for analyzing the normal transmitter role of glutamic acid in reflex voiding.

Analysis of Variance↗

PubMed1994

Localization of NADPH diaphorase in the lumbosacral spinal cord and dorsal root ganglia of the cat.

The distribution of NADPH-d activity in the spinal cord and dorsal root ganglia of the cat was studied to evaluate the role of nitric oxide in lumbosacral afferent and spinal autonomic pathways. At all levels of the spinal cord NADPH-d staining was present in neurons and fibers in the superficial dorsal horn and in neurons around the central canal and in the dorsal commissure. In addition, the sympathetic autonomic nucleus in the rostral lumbar segments exhibited prominent NADPH-d cellular staining whereas the parasympathetic nucleus in the sacral segments was not well stained. The most prominent NADPH-d activity in the sacral segments occurred in fibers extending from Lissauer's tract through laminae I along the lateral edge of the dorsal horn to lamina V and the region of the sacral parasympathetic nucleus. These fibers were very similar to VIP-containing and pelvic nerve afferent projections in the same region. They were prominent in the S1-S3 segments but not in adjacent segments (L6-L7 and Cx1) or in thoracolumbar and cervical segments. NADPH-d activity and VIP immunoreactivity in Lissauer's tract and the lateral dorsal horn were eliminated or greatly reduced after dorsal-ventral rhizotomy (S1-S3), indicating the fibers represent primary afferent projections. A population of small diameter afferent neurons in the L7-S2 dorsal root ganglia were intensely stained for NADPH-d. The functional significance of the NADPH-d histochemical stain remains to be determined; however, if NADPH-d is nitric oxide synthase then this would suggest that nitric oxide may function as a transmitter in thoracolumbar sympathetic preganglionic efferent pathways and in sacral parasympathetic afferent pathways in the cat.

Afferent Pathways↗

PubMed1994

Effect of urinary diversion on the recovery of micturition reflexes after spinal cord injury in the rat.

Patients with suprasacral spinal cord injury usually exhibit severe lower urinary tract dysfunction, which is generally attributed to loss of supraspinal input to the spinal micturition centers. However, some of the dysfunction may also arise secondary to bladder overdistension during the initial period of bladder areflexia. This study evaluated the consequences of bladder overdistension by performing urinary diversion in spinalized (T8-T10) rats. Bladder function was evaluated in urethane-anesthetized control and spinalized animals approximately 24 days after diversion. Chronically spinalized diverted and nondiverted rats exhibited similar micturition dysfunction: bladder/sphincter dyssynergia, incomplete voiding and ineffective (nonvoiding) bladder contractions. These data indicate that neither the condition of the bladder (such as chronic overdistension or bladder hypertrophy) nor afferent input from the bladder to the spinal cord dictates the development of reflex micturition and micturition dysfunction after spinal cord injury, suggesting that the dysfunction is intrinsic to spinal micturition reflex pathways.

Animals↗