Nicotinic acetylcholine receptors in the autonomic control of bladder function

α7 nicotinic receptors play a role in regulation of cardiac hemodynamics

The α7 nicotinic receptors (NR) have been confirmed in the heart but their role in cardiac functions has been contradictory. To address these contradictory findings, we analyzed cardiac functions in α7 NR knockout mice (α7-/-) in vivo and ex vivo in isolated hearts. A standard limb leads electrocardiogram was used, and the pressure curves were recorded in vivo, in Arteria carotis and in the left ventricle, or ex vivo, in the left ventricle of the spontaneously beating isolated hearts perfused following Langedorff's method. Experiments were performed under basic conditions, hypercholinergic conditions, and adrenergic stress. The relative expression levels of α and β NR subunits, muscarinic receptors, β1 adrenergic receptors, and acetylcholine life cycle markers were determined using RT-qPCR. Our results revealed a prolonged QT interval in α7-/- mice. All in vivo hemodynamic parameters were preserved under all studied conditions. The only difference in ex vivo heart rate between genotypes was the loss of bradycardia in prolonged incubation of isoproterenol-pretreated hearts with high doses of acetylcholine. In contrast, left ventricular systolic pressure was lower under basal conditions and showed a significantly higher increase during adrenergic stimulation. No changes in mRNA expression were observed. In conclusion, α7 NR has no major effect on heart rate, except when stressed hearts are exposed to a prolonged hypercholinergic state, suggesting a role in acetylcholine spillover control. In the absence of extracardiac regulatory mechanisms, left ventricular systolic impairment is revealed.

Nerve transfer for restoration of lower motor neuron-lesioned bladder, urethral, and anal sphincter function in a dog model. Part 3. nicotinic receptor characterization

Very little is known about the physiological role of nicotinic receptors in canine bladders, although functional nicotinic receptors have been reported in bladders of many species. Utilizing in vitro methods, we evaluated nicotinic receptors mediating bladder function in dogs: control (9 female and 11 male normal controls, 5 sham operated), Decentralized (9 females, decentralized 6-21 mo), and obturator-to-pelvic nerve transfer reinnervated (ObNT-Reinn; 9 females; decentralized 9-13 mo, then reinnervated with 8-12 mo recovery). Muscle strips were collected, mucosa-denuded, and mounted in muscle baths before incubation with neurotransmitter antagonists, and contractions to the nicotinic receptor agonist epibatidine were determined. Strip response to epibatidine, expressed as percent potassium chloride, was similar (∼35% in controls, 30% in Decentralized, and 24% in ObNT-Reinn). Differentially, epibatidine responses in Decentralized and ObNT-Reinn bladder strips were lower than controls after tetrodotoxin (TTX, a sodium channel blocker that inhibits axonal action potentials). Yet, in all groups, epibatidine-induced strip contractions were similarly inhibited by mecamylamine and hexamethonium (ganglionic nicotinic receptor antagonists), SR 16584 (α3β4 neuronal nicotinic receptor antagonist), atracurium and tubocurarine (neuromuscular nicotinic receptor antagonists), and atropine (muscarinic receptor antagonist), indicating that nicotinic receptors (particularly α3β4 subtypes), neuromuscular and muscarinic receptors play roles in bladder contractility. In control bladder strips, since tetrodotoxin did not inhibit epibatidine contractions, nicotinic receptors are likely located on nerve terminals. The tetrodotoxin inhibition of epibatidine-induced contractions in Decentralized and ObNT-Reinn suggests a relocation of nicotinic receptors from nerve terminals to more distant axonal sites, perhaps as a compensatory mechanism to recover bladder function.

Possible involvement of brain hydrogen sulphide in the inhibition of the rat micturition reflex induced by activation of brain alpha7 nicotinic acetylcholine receptors

We previously reported that brain α7 nicotinic acetylcholine receptors inhibited the rat micturition reflex. To elucidate the mechanisms underlying this inhibition, we focused on the relationship between α7 nicotinic acetylcholine receptors and hydrogen sulphide (H₂S) because we found that H₂S also inhibits the rat micturition reflex in the brain. Therefore, we investigated whether H₂S is involved in the inhibition of the micturition reflex induced by the activation of α7 nicotinic acetylcholine receptors in the brain. Cystometry was performed in male Wistar rats under urethane anesthesia (0.8 g/kg, ip) to examine the effects of icv pre-treated GYY4137 (H₂S donor, 1 or 3 nmol/rat) or aminooxyacetic acid (AOAA; non-selective H₂S synthesis inhibitor, 3 or 10 μg/rat) on PHA568487 (α7 nicotinic acetylcholine receptor agonist, icv)-induced prolongation of intercontraction intervals. PHA568487 administration at a lower dose (0.3 nmol/rat, icv) had no significant effect on intercontraction intervals, while under pre-treatment with GYY4137 (3 nmol/rat icv), PHA568487 (0.3 nmol/rat, icv) significantly prolonged intercontraction intervals. PHA568487 at a higher dose (1 nmol/rat, icv) induced intercontraction interval prolongation, and the PHA568487-induced prolongation was significantly suppressed by AOAA (10 μg/rat, icv). The AOAA-induced suppression of the PHA568487-induced intercontraction interval prolongation was negated by supplementing H₂S via GYY4137 at a lower dose (1 nmol/rat, icv) in the brain. GYY4137 or AOAA alone showed no significant effect on intercontraction intervals at each dose used in this study. These findings suggest a possible involvement of brain H₂S in inhibiting the rat micturition reflex induced by activation of brain alpha7 nicotinic acetylcholine receptors.

Dog and human bladders have different neurogenic and nicotinic responses in inner versus outer detrusor muscle layers

The aim of this study was to investigate layer and species variations in detrusor muscle strip responses to myogenic, neurogenic, and nicotinic, and muscarinic receptor stimulations. Strips from bladders of 9 dogs and 6 human organ transplant donors were dissected from inner and outer longitudinal muscle layers, at least 1 cm above urethral orifices. Strips were mounted in muscle baths and maximal responses to neurogenic stimulation using electrical field stimulation (EFS) and myogenic stimulation using potassium chloride (KCl, 120 mM) determined. After washing and re-equilibration was completed, responses to nicotinic receptor agonist epibatidine (10 μM) were determined followed by responses to EFS and muscarinic receptor agonist bethanechol (30 μM) in continued presence of epibatidine. Thereafter, strips and full-thickness bladder sections from four additional dogs and three human donors were examined for axonal density and intramural ganglia. In dog bladders, contractions to KCl, epibatidine, and bethanechol were 1.5- to 2-fold higher in the inner longitudinal muscle layer, whereas contractions to EFS were 1.5-fold higher in the outer (both pre- and post-epibatidine). Human bladders showed 1.2-fold greater contractions to epibatidine in the inner layer and to EFS in the outer, yet no layer differences to KCl or bethanechol were noted. In both species, axonal density was 2- to 2.5-fold greater in the outer layer. Dogs had more intramural ganglia in the adventitia/serosa layer, compared with more internal layers and to humans. These findings indicate several layer-dependent differences in receptor expression or distribution, and neurogenic responses in dog and human detrusor muscles, and myogenic/muscarinic differences between dog versus humans.

Psychological/mental stress-induced effects on urinary function: Possible brain molecules related to psychological/mental stress-induced effects on urinary function

Exposure to psychological/mental stress can affect urinary function, and lead to and exacerbate lower urinary tract dysfunctions. There is increasing evidence showing stress-induced changes not only at phenomenological levels in micturition, but also at multiple levels, lower urinary tract tissues, and peripheral and central nervous systems. The brain plays crucial roles in the regulation of the body's responses to stress; however, it is still unclear how the brain integrates stress-related information to induce changes at these multiple levels, thereby affecting urinary function and lower urinary tract dysfunctions. In this review, we introduce recent urological studies investigating the effects of stress exposure on urinary function and lower urinary tract dysfunctions, and our recent studies exploring "pro-micturition" and "anti-micturition" brain molecules related to stress responses. Based on evidence from these studies, we discuss the future directions of central neurourological research investigating how stress exposure-induced changes at peripheral and central levels affect urinary function and lower urinary tract dysfunctions. Brain molecules that we explored might be entry points into dissecting the stress-mediated process for modulating micturition.

Stimulation of brain α7-nicotinic acetylcholine receptors suppresses the rat micturition through brain GABAergic receptors

Brain nicotinic acetylcholine receptors (nAChRs) reportedly suppress the micturition, but the mechanisms responsible for this suppression remain unclear. We previously reported that intracerebroventricularly administered (±)-epibatidine (non-selective nAChR agonist) activated the sympatho-adrenomedullary system, which can affect the micturition. Therefore, we investigated (1) whether intracerebroventricularly administered (±)-epibatidine-induced effects on the micturition were dependent on the sympatho-adrenomedullary system, and (2) brain nAChR subtypes involved in the (±)-epibatidine-induced effects in urethane-anesthetized male Wistar rats. Plasma noradrenaline and adrenaline (catecholamines) were measured just before and 5 min after (±)-epibatidine administration. Evaluation of urodynamic parameters, intercontraction intervals (ICI) and maximal voiding pressure (MVP) by cystometry was started 1 h before (±)-epibatidine administration or intracerebroventricular pretreatment with other drugs and continued 1 h after (±)-epibatidine administration. Intracerebroventricularly administered (±)-epibatidine elevated plasma catecholamines and prolonged ICI without affecting MVP, and these changes were suppressed by intracerebroventricularly pretreated mecamylamine (non-selective nAChR antagonist). Acute bilateral adrenalectomy abolished the (±)-epibatidine-induced elevation of plasma catecholamines, but had no effect on the (±)-epibatidine-induced ICI prolongation. The latter was suppressed by intracerebroventricularly pretreated methyllycaconitine (selective α7-nAChR antagonist), SR95531 (GABAA antagonist), and SCH50911 (GABAB antagonist), but not by dihydro-β-erythroidine (selective α4β2-nAChR antagonist). Intracerebroventricularly administered PHA568487 (selective α7-nAChR agonist) prolonged ICI without affecting MVP, similar to (±)-epibatidine. These results suggest that stimulation of brain α7-nAChRs suppresses the rat micturition through brain GABAA/GABAB receptors, independently of the sympatho-adrenomedullary outflow modulation.

Cardiac nicotinic receptors show β-subunit-dependent compensatory changes

Nicotinic receptors (NRs) play an important role in the cholinergic regulation of heart functions, and converging evidence suggests a diverse repertoire of NR subunits in the heart. A recent hypothesis about the plasticity of β NR subunits suggests that β2-subunits and β4-subunits may substitute for each other. In our study, we assessed the hypothetical β-subunit interchangeability in the heart at the level of mRNA. Using two mutant mice strains lacking β2 or β4 NR subunits, we examined the relative expression of NR subunits and other key cholinergic molecules. We investigated the physiology of isolated hearts perfused by Langendorff's method at basal conditions and after cholinergic and/or adrenergic stimulation. Lack of β2 NR subunit was accompanied with decreased relative expression of β4-subunits and α3-subunits. No other cholinergic changes were observed at the level of mRNA, except for increased M3 and decreased M4 muscarinic receptors. Isolated hearts lacking β2 NR subunit showed different dynamics in heart rate response to indirect cholinergic stimulation. In hearts lacking β4 NR subunit, increased levels of β2-subunits were observed together with decreased mRNA for acetylcholine-synthetizing enzyme and M1 and M4 muscarinic receptors. Changes in the expression levels in β4^-/- hearts were associated with increased basal heart rate and impaired response to a high dose of acetylcholine upon adrenergic stimulation. In support of the proposed plasticity of cardiac NRs, our results confirmed subunit-dependent compensatory changes to missing cardiac NRs subunits with consequences on isolated heart physiology.NEW & NOTEWORTHY In the present study, we observed an increase in mRNA levels of the β2 NR subunit in β4^-/- hearts but not vice versa, thus supporting the hypothesis of β NR subunit plasticity that depends on the specific type of missing β-subunit. This was accompanied with specific cholinergic adaptations. Nevertheless, isolated hearts of β4^-/- mice showed increased basal heart rate and a higher sensitivity to a high dose of acetylcholine upon adrenergic stimulation.

Nicotinic Acetylcholine Receptor Involvement in Inflammatory Bowel Disease and Interactions with Gut Microbiota

The gut-brain axis describes a complex interplay between the central nervous system and organs of the gastrointestinal tract. Sensory neurons of dorsal root and nodose ganglia, neurons of the autonomic nervous system, and immune cells collect and relay information about the status of the gut to the brain. A critical component in this bi-directional communication system is the vagus nerve which is essential for coordinating the immune system’s response to the activities of commensal bacteria in the gut and to pathogenic strains and their toxins. Local control of gut function is provided by networks of neurons in the enteric nervous system also called the ‘gut-brain’. One element common to all of these gut-brain systems is the expression of nicotinic acetylcholine receptors. These ligand-gated ion channels serve myriad roles in the gut-brain axis including mediating fast synaptic transmission between autonomic pre- and postganglionic neurons, modulation of neurotransmitter release from peripheral sensory and enteric neurons, and modulation of cytokine release from immune cells. Here we review the role of nicotinic receptors in the gut-brain axis with a focus on the interplay of these receptors with the gut microbiome and their involvement in dysregulation of gut function and inflammatory bowel diseases.

Early life voiding dysfunction leads to lower urinary tract dysfunction through alteration of muscarinic and purinergic signaling in the bladder

Lower urinary tract dysfunction (LUTD) is a common problem in children and constitutes up to 40% of pediatric urology clinic visits. Improved diagnosis and interventions have been leading to better outcomes in many patients, whereas some children are left untreated or do not respond to the treatment successfully. In addition, many of these patients are lost by the pediatric urologists during their teenage years, and the outcome in later life largely remains unidentified. Studies suggest childhood LUTD is associated with subsequent adult urinary tract symptoms. However, whether and how early life LUTD attributes to urinary symptoms in those patients later in life remains to be elucidated. In the current study, we investigated the effects of early life voiding perturbation on bladder function using a neonatal maternal separation (NMS) protocol in mice. The NMS group displayed a delayed development of voluntary voiding behavior, a significant reduction of functional bladder capacity, and bladder overactivity compared with control mice later in life. In vitro evaluation of detrusor smooth muscle and molecular study showed a decrease in muscarinic contribution alongside an increase in purinergic contribution in detrusor contractility in NMS mice compared with control group. These results suggest that early life bladder dysfunction interfered with the normal maturation of the voluntary micturition control and facilitated LUTD in a later stage, which is at least partly attributed to an alteration of muscarinic and purinergic signaling in the urinary bladder.

A four-component model of the action potential in mouse detrusor smooth muscle cell

Background and hypothesis

Detrusor smooth muscle cells (DSMCs) of the urinary bladder are electrically connected to one another via gap junctions and form a three dimensional syncytium. DSMCs exhibit spontaneous electrical activity, including passive depolarizations and action potentials. The shapes of spontaneous action potentials (sAPs) observed from a single DSM cell can vary widely. The biophysical origins of this variability, and the precise components which contribute to the complex shapes observed are not known. To address these questions, the basic components which constitute the sAPs were investigated. We hypothesized that linear combinations of scaled versions of these basic components can produce sAP shapes observed in the syncytium.

Methods and results

The basic components were identified as spontaneous evoked junction potentials (sEJP), native AP (nAP), slow after hyperpolarization (sAHP) and very slow after hyperpolarization (vsAHP). The experimental recordings were grouped into two sets: a training data set and a testing data set. A training set was used to estimate the components, and a test set to evaluate the efficiency of the estimated components. We found that a linear combination of the identified components when appropriately amplified and time shifted replicated various AP shapes to a high degree of similarity, as quantified by the root mean square error (RMSE) measure.

Conclusions

We conclude that the four basic components—sEJP, nAP, sAHP, and vsAHP—identified and isolated in this work are necessary and sufficient to replicate all varieties of the sAPs recorded experimentally in DSMCs. This model has the potential to generate testable hypotheses that can help identify the physiological processes underlying various features of the sAPs. Further, this model also provides a means to classify the sAPs into various shape classes.

Synthesis and biological evaluation of 8-hydroxy-2,7-naphthyridin-2-ium salts as novel inhibitors of acetylcholinesterase (AChE) and butyrylcholinesterase (BChE)

By analogy with the natural product chelerythrine, which has been identified as an inhibitor of both acetylcholinesterase (AChE) and butyrylcholinesterase (BChE), we prepared a small series of 8-hydroxy-2,7-naphthyridin-2-ium salts. Spectroscopic analyses allowed us to elucidate the zwitterionic nature of 2,7-naphthyridin-1(7H)-ones, the neutral state of 8-hydroxy-2,7-naphthyridin-2-ium salts. Among the tested compounds, we identified dual inhibitors of AChE and BChE as well as an inhibitor showing a preferential inhibition of AChE over BChE. By in vitro characterization in combination with docking studies, we were able to identify structural features that influence the biological activity of 8-hydroxy-2,7-naphthyridin-2-ium salts.

Lower urinary tract dysfunction in patients with peripheral nervous system lesions

The prevalence of lower urinary tract (LUT) dysfunction in peripheral nervous system (PNS) disorders is larger than in comparable control populations. This is particularly true for polyneuropathies with autonomic nervous system involvement, and for localized lesions with LUT innervation. LUT symptoms may be the guide to the diagnosis of processes localized in the lumbosacral spinal canal (as in cauda equina syndrome), and in the pelvis. Typical LUT dysfunctions (LUTD) caused by PNS involvement include bladder and sphincter hypoactivity with poor emptying, and incontinence. Paradoxically, bladder overactivity may also occur in pure PNS lesions. The acute cauda equina syndrome is an emergency requiring magnetic resonance imaging and surgery; in chronic neurogenic LUTD due to PNS involvement, the diagnosis of the lesion may be clarified by clinical neurophysiologic testing. Other important causes of neurogenic LUT dysfunction are perineoabdominal and pelvic surgeries. Surgeons are devising nerve-sparing techniques to prevent such major and often persistent complications in patients who are otherwise cured of the underlying disease. LUTD significantly affects the quality of life in patients and may lead to recurring urinary infections and upper urinary tract involvement. Thorough assessment of LUT function by urodynamics may be necessary in patients who are not improved by simple conservative measures.

Role of Nicotinic Acetylcholine Receptor α3 and α7 Subunits in Detrusor Overactivity Induced by Partial Bladder Outlet Obstruction in Rats

Purpose:

To investigate the role of α3 and α7 nicotinic acetylcholine receptor subunits (nAChRs) in the bladder, using a rat model with detrusor overactivity induced by partial bladder outlet obstruction (BOO).

Methods:

Forty Sprague-Dawley rats were used: 10 were sham-operated (control group) and 30 were observed for 3 weeks after partial BOO. BOO-induced rats were further divided into 3 groups: Two groups of 10 rats each received intravesicular infusions with hexamethonium (HM group; n=10) or methyllycaconitine (MLC group; n=10), which are antagonists for α3 and α7 nAChRs, respectively. The remaining BOO-induced rats received only saline infusion (BOO group; n=10). Based on the contraction interval measurements using cystometrogram, the contraction pressure and nonvoiding bladder contractions were compared between the control and the three BOO-induced groups. Immunofluorescent staining and Western blotting were used to analyze α3 and α7 nAChRs levels.

Results:

The contraction interval of the MLC group was higher than that of the BOO group (P<0.05). Nonvoiding bladder contraction almost disappeared in the HM and MLC groups. Contraction pressure increased in the BOO group (P<0.05) compared with the control group and decreased in the HM and MLC groups compared with the BOO group (P<0.05). Immunofluorescence staining showed that the α3 nAChR signals increased in the urothelium, and the α7 nAChR signals increased in the urothelium and detrusor muscle of the BOO group compared with the control group. Western blot analysis showed that both α3 and α7 nAChR levels increased in the BOO group (P<0.05).

Conclusions:

Alpha3 and α7 nAChRs are associated with detrusor overactivity induced by BOO. Furthermore, nAChR antagonists could help in clinically improving detrusor overactivity.

Neuromuscular nicotinic receptors mediate bladder contractions following bladder reinnervation with somatic to autonomic nerve transfer after decentralization by spinal root transection

PURPOSE

We investigated whether the reinnervated neuronal pathway mediates contraction via the same neurotransmitter and receptor mechanisms as the original pathway.

MATERIALS AND METHODS

After decentralizing the bladder by transecting the sacral roots in dogs we performed peripheral nerve transfer, including bilateral genitofemoral to pelvic nerve transfer and unilateral left femoral nerve to bilateral pelvic nerve transfer. Reinnervation was assessed 7.5 months postoperatively by monitoring bladder pressure during electrical stimulation of the transferred nerves, spinal ventral roots and spinal cord.

RESULTS

Of the 17 dogs with genitofemoral to pelvic nerve transfer 14 (82%) demonstrated functional bladder reinnervation as evidenced by increased bladder pressure during stimulation of the transferred genitofemoral nerve, or L3 or L4 spinal ventral roots. Lumbar spinal cord stimulation caused increased bladder pressure in 9 of 10 dogs (90%) with unilateral left femoral nerve to bilateral pelvic nerve transfer. Succinylcholine virtually eliminated the bladder pressure increases induced by electrical stimulation of the transferred somatic nerves or of the lumbar spinal segments that contribute axons to these donor nerves. In unoperated or sham operated controls succinylcholine had no effect on nerve evoked bladder pressure increases but it substantially decreased the urethral and anal sphincter pressure induced by stimulating the lumbosacral spinal cord or the S2-S3 spinal ventral roots. The reinnervated detrusor muscles of dogs with genitofemoral to pelvic nerve transfer and unilateral left femoral nerve to bilateral pelvic nerve transfer also showed increased α1 nicotinic receptor subunit immunoreactivity in punctate dots on detrusor muscle fascicles and in neuronal cell bodies. This staining was not observed in controls.

CONCLUSIONS

Succinylcholine sensitive nicotinic receptors, which normally mediate only skeletal muscle neuromuscular junction neurotransmission, appeared in the new neuronal pathway after genitofemoral to pelvic and unilateral femoral nerve to bilateral pelvic nerve transfer. This suggests end organ neuroplasticity after reinnervation by somatic motor axons.

Potential therapeutic uses of mecamylamine and its stereoisomers

Mecamylamine (3-methylaminoisocamphane hydrochloride) is a nicotinic parasympathetic ganglionic blocker, originally utilized as a therapeutic agent to treat hypertension. Mecamylamine administration produces several deleterious side effects at therapeutically relevant doses. As such, mecamylamine's use as an antihypertensive agent was phased out, except in severe hypertension. Mecamylamine easily traverses the blood-brain barrier to reach the central nervous system (CNS), where it acts as a nicotinic acetylcholine receptor (nAChR) antagonist, inhibiting all known nAChR subtypes. Since nAChRs play a major role in numerous physiological and pathological processes, it is not surprising that mecamylamine has been evaluated for its potential therapeutic effects in a wide variety of CNS disorders, including addiction. Importantly, mecamylamine produces its therapeutic effects on the CNS at doses 3-fold lower than those used to treat hypertension, which diminishes the probability of peripheral side effects. This review focuses on the pharmacological properties of mecamylamine, the differential effects of its stereoisomers, S(+)- and R(-)-mecamylamine, and the potential for effectiveness in treating CNS disorders, including nicotine and alcohol addiction, mood disorders, cognitive impairment and attention deficit hyperactivity disorder.

Abnormal social behavior in nicotinic acetylcholine receptor β4 subunit-null mice

INTRODUCTION

Tobacco addiction has a strong social component. Therefore, nicotinic acetylcholine receptors (nAChR) may influence social behavior. Because the β4 nicotinic receptor subunit is important for possibly related behaviors, such as anxiety-like behavior and the effects of nicotine, we studied the social behavior of mice null for the β4 nAChR subunit.

METHODS

To measure social behavior, we used the intruder test for social memory in wild-type and littermate β4 null mice. In addition, we used a nonsocial olfactory memory test as a control.

RESULTS

In the intruder test, β4 null mice showed social amnesia: Wild-type mice spent less time actively interacting with a younger intruder on Day 2 than on Day 1, but β4 null mice interacted for a similar time on both days. In the nonsocial olfactory memory test, control littermates and β4 null mice learnt the associations to a similar extent, showing that the amnesic phenotype in the intruder test is specific for social settings.

CONCLUSIONS

We conclude that nAChRs that contain the β4 subunit are important for social behaviors. As those receptors are necessary to observe several effects of nicotine including withdrawal, it is tempting to speculate that the social component of tobacco use is related to the same neuronal circuits responsible for continuing tobacco use in smokers.

Pharmacokinetic study of nicotine and its metabolite cotinine to clarify possible association between smoking and voiding dysfunction in rats using UPLC/ESI-MS

The present study was undertaken to clarify the possible association between nicotine intake/cigarette smoking and detrusor instability. For pharmacokinetic characterization of nicotine and cotinine (a major and pharmacologically less active metabolite of nicotine), a rapid ultra-performance liquid chromatography/electrospray ionization-mass spectrometry (UPLC/ESI-MS) method was developed that requires only a small amount of sample and simple pretreatment. The UPLC/ESI-MS method was validated with a focus on specificity, sensitivity (limit of detection, 2.5 ng/mL; limit of quantification, 5 ng/mL), linearity (r > 0.998), accuracy (97.2-102.8%), precision (relative standard deviation <8%) and robustness in accordance with ICH guidelines (Q2B Validation of Analytical Procedures: Methodology). The developed method was successfully applied to determine nicotine and cotinine levels in rat biological samples such as plasma, urine and several tissues. After subcutaneous administration of nicotine ditartrate (2 mg/kg of body weight) in rats, the absorbed nicotine was rapidly and extensively metabolized into cotinine. However, nicotine was found to be predominant in cortex and bladder, where nicotinic acetylcholine receptors were expressed for neuronal control of voiding function. Repeated administration of nicotine led to a ca. 3-fold higher accumulation of nicotine than that of cotinine in rat urine. The results of the pharmacokinetic study using the UPLC/ESI-MS method further support the possible involvement of nicotine in increased risk of urinary dysfunction in smokers.

Neural control of the lower urinary tract: peripheral and spinal mechanisms

This review deals with individual components regulating the neural control of the urinary bladder. This article will focus on factors and processes involved in the two modes of operation of the bladder: storage and elimination. Topics included in this review include: (1) The urothelium and its roles in sensor and transducer functions including interactions with other cell types within the bladder wall ("sensory web"), (2) The location and properties of bladder afferents including factors involved in regulating afferent sensitization, (3) The neural control of the pelvic floor muscle and pharmacology of urethral and anal sphincters (focusing on monoamine pathways), (4) Efferent pathways to the urinary bladder, and (5) Abnormalities in bladder function including mechanisms underlying comorbid disorders associated with bladder pain syndrome and incontinence.

Roles of Peripheral and Central Nicotinic Receptors in the Micturition Reflex in Rats

PURPOSE

We investigated the effects of nicotinic acetylcholine receptor activation in the bladder and central nervous system on the micturition reflex in urethane anesthetized rats.

MATERIALS AND METHODS

The effects of nicotinic acetylcholine receptor activation on bladder activity were examined during continuous infusion cystometrogram. Nicotine with or without the nicotinic acetylcholine receptor antagonist mecamylamine (Sigma Chemical Co., St. Louis, Missouri) was administered intravesically, intrathecally or intracerebroventricularly in normal or capsaicin pretreated rats. We also examined nicotine induced responses in dissociated bladder afferent neurons from L6 to S1 dorsal root ganglia that were sensitive to capsaicin using whole cell patch clamp recordings.

RESULTS

Intravesical nicotine (1 to 10 mM) significantly decreased intercontraction intervals in dose dependent fashion. This excitatory effect was abolished by co-application of mecamylamine (3 mM) as well as by capsaicin pretreatment. On patch clamp recordings 300 muM nicotine evoked rapid inward currents that were antagonized by mecamylamine in capsaicin sensitive bladder afferent neurons. Intrathecal and intracerebroventricular administration of nicotine (10 mug) decreased and increase intercontraction intervals, respectively. Each effect was antagonized by mecamylamine (50 mug) administered intrathecally and intracerebroventricularly. The spinal excitatory effect was significantly inhibited by the N-methyl-D-aspartate receptor antagonist (+)-MK-801 hydrogen maleate (20 mug) given intrathecally or by capsaicin pretreatment, although the effects of capsaicin pretreatment were significantly smaller than those of (+)-MK-801 hydrogen maleate.

CONCLUSIONS

These results indicate that nicotinic acetylcholine receptor activation in capsaicin sensitive C-fiber afferents in the bladder can induce detrusor overactivity. In the central nervous system nicotinic acetylcholine receptor activation in the spinal cord and brain has an excitatory and an inhibitory effect on the micturition reflex, respectively. In addition, the nicotine induced spinal excitatory effect may be mediated by the activation of glutamatergic mechanisms.

Expression of functional nicotinic acetylcholine receptors in rat urinary bladder epithelial cells

Although nicotinic acetylcholine receptors in both the central and peripheral nervous systems play a prominent role in the control of urinary bladder function, little is known regarding expression or function of nicotinic receptors in the bladder epithelium, or urothelium. Nicotinic receptors have been described in epithelial cells lining the upper gastrointestinal tract, respiratory tract, and the skin. Thus the present study examined the expression and functionality of nicotinic receptors in the urothelium, as well as the effects of stimulation of nicotinic receptors on the micturition reflex. mRNA for the alpha3, alpha5, alpha7, beta3, and beta4 nicotinic subunits was identified in rat urothelial cells using RT-PCR. Western blotting also confirmed urothelial expression of the alpha3- and alpha7-subunits. Application of nicotine (50 nM) to cultured rat urothelial cells elicited an increase in intracellular Ca2+ concentration, indicating that at least some of the subunits form functional channels. These effects were blocked by the application of the nicotinic antagonist hexamethonium. During in vivo bladder cystometrograms in urethane-anesthetized rats, intravesical administration of nicotine, choline, or the antagonists methyllycaconitine citrate and hexamethonium elicited changes in voiding parameters. Intravesical nicotine (50 nM, 1 microM) increased the intercontraction interval. Intravesical choline (1-100 microM) also affected bladder reflexes similarly, suggesting that alpha7 nicotinic receptors mediate this effect. Intravesical administration of hexamethonium (1-100 microM) potentiated the nicotine-induced changes in bladder reflexes. Methyllycaconitine citrate, a specific alpha7-receptor antagonist, prevented nicotine-, choline-, and hexamethonium-induced bladder inhibition. These results are the first indication that stimulation of nonneuronal nicotinic receptors in the bladder can affect micturition.

Lower core body temperature and attenuated nicotine-induced hypothermic response in mice lacking the beta4 neuronal nicotinic acetylcholine receptor subunit

Diverse physiological and pathological effects of nicotine, including the alteration of body temperature, are presumably mediated by neuronal nicotinic acetylcholine receptors (nAChR). Previous studies have suggested the involvement of distinct nAChR subunits in nicotine-induced thermoregulation. We studied genetically manipulated knockout mice lacking the alpha7, alpha5 or beta4 subunit genes, in order to assess the effects of subunit deficiency on temperature regulation. Using a telemetry system, core body temperature was monitored continuously prior to and following nicotine administration in mutant mice and in wild-type littermates. Mice lacking in the beta4 nAChR subunit gene had significantly lower baseline core body temperature than all other mouse strains studied. beta4 null mice also demonstrated a reduced nicotine-induced hypothermic response and impaired desensitization following repeat nicotine exposure. These findings suggest the involvement of the beta4 nAChR subunit in both core body temperature homeostasis and nicotine-elicited thermo-alterations in mice.

The alpha3 and beta4 nicotinic acetylcholine receptor subunits are necessary for nicotine-induced seizures and hypolocomotion in mice

Binding of nicotine to nicotinic acetylcholine receptors (nAChRs) elicits a series of dose-dependent behaviors that go from altered exploration, sedation, and tremors, to seizures and death. nAChRs are pentameric ion channels usually composed of alpha and beta subunits. A gene cluster comprises the alpha3, alpha5 and beta4 subunits, which coassemble to form functional receptors. We examined the role of the beta4 subunits in nicotine-induced seizures and hypolocomotion in beta4 homozygous null (beta4 -/-) and alpha3 heterozygous (+/-) mice. beta4 -/- mice were less sensitive to the effects of nicotine both at low doses, measured as decreased exploration in an open field, and at high doses, measured as sensitivity to nicotine-induced seizures. Using in situ hybridization probes for the alpha3 and alpha5 subunits, we showed that alpha5 mRNA levels are unchanged, whereas alpha3 mRNA levels are selectively decreased in the mitral cell layer of the olfactory bulb, and the inferior and the superior colliculus of beta4 -/- brains. alpha3 +/- mice were partially resistant to nicotine-induced seizures when compared to wild-type littermates. mRNA levels for the alpha5 and the beta4 subunits were unchanged in alpha3 +/- brains. Together, these results suggest that the beta4 and the alpha3 subunits are mediators of nicotine-induced seizures and hypolocomotion.

Nicotinic acetylcholine receptors: from structure to brain function

Nicotinic acetylcholine receptors (nAChRs) are ligand-gated ion channels and can be divided into two groups: muscle receptors, which are found at the skeletal neuromuscular junction where they mediate neuromuscular transmission, and neuronal receptors, which are found throughout the peripheral and central nervous system where they are involved in fast synaptic transmission. nAChRs are pentameric structures that are made up of combinations of individual subunits. Twelve neuronal nAChR subunits have been described, alpha2-alpha10 and beta2-beta4; these are differentially expressed throughout the nervous system and combine to form nAChRs with a wide range of physiological and pharmacological profiles. The nAChR has been proposed as a model of an allosteric protein in which effects arising from the binding of a ligand to a site on the protein can lead to changes in another part of the molecule. A great deal is known about the structure of the pentameric receptor. The extracellular domain contains binding sites for numerous ligands, which alter receptor behavior through allosteric mechanisms. Functional studies have revealed that nAChRs contribute to the control of resting membrane potential, modulation of synaptic transmission and mediation of fast excitatory transmission. To date, ten genes have been identified in the human genome coding for the nAChRs. nAChRs have been demonstrated to be involved in cognitive processes such as learning and memory and control of movement in normal subjects. Recent data from knockout animals has extended the understanding of nAChR function. Dysfunction of nAChR has been linked to a number of human diseases such as schizophrenia, Alzheimer's and Parkinson's diseases. nAChRs also play a significant role in nicotine addiction, which is a major public health concern. A genetically transmissible epilepsy, ADNFLE, has been associated with specific mutations in the gene coding for the alpha4 or beta2 subunits, which leads to altered receptor properties.

Deficiency of nicotinic acetylcholine receptor beta 4 subunit causes autonomic cardiac and intestinal dysfunction

Neuronal nicotinic acetylcholine receptors (nAChR) are composed of 12 subunits (alpha 2-alpha 10 and beta 2-beta 4), which play the central role in autonomic transmission. beta 4 subunits are abundantly expressed in autonomic ganglia, forming acetylcholine binding sites and ion channels with alpha 3 or alpha 3 and alpha 5 subunits as pentameric receptors. To investigate the physiological and pharmacological properties of beta 4 subunits in autonomic ganglia, we measured autonomic functions in knockout mice lacking nAChR subunit beta 4 (beta 4(-/-)) and wild-type mice. beta 4(-/-) mice had an attenuated bradycardiac response to high frequency (60 pulse/s) vagal stimulation, as well as an increased sensitivity to hexamethonium blockade at low dose (3 mg/kg) and a reduced ileal contractile response to the nicotinic agonists cytisine, dimethylphenylpiperazinium iodide, nicotine (10 mg/kg each), and epibatidine (0.1 mg/kg). The results suggest that beta 4 subunits are important components of nAChRs in autonomic ganglia. Deficiency of beta 4 subunits altered ion channel properties, conductance, and sensitivity and affinity of receptors to agonists and antagonists, affecting ganglionic transmission.

Nicotinic mechanisms in the autonomic control of organ systems

Most visceral organs are under the control of the autonomic nervous system (ANS). Information on the state and function of these organs is constantly relayed to the central nervous system (CNS) by sensory afferent fibers. The CNS integrates the sensory inputs and sends neural commands back to the organ through the ANS. The autonomic ganglia are the final site for the integration of the message traveling from the CNS. Nicotinic acetylcholine receptors (nAChRs) are the main mediators of fast synaptic transmission in ganglia, and therefore, are key molecules for the processing of neural information in the ANS. This review focuses on the role of nAChRs in the control of organ systems such as heart, gut, and bladder. The autonomic control of these organ systems is discussed in the light of the results obtained from the analysis of mice carrying mutations targeted to nAChR subunits expressed in the ANS.

The role of neuronal nicotinic acetylcholine receptor subunits in autonomic ganglia: lessons from knockout mice

Neuronal nicotinic acetylcholine receptors (nAChR), composed of 12 subunits (alpha2-alpha10, beta2-beta4), are expressed in autonomic ganglia, playing a central role in autonomic transmission. The repertoire of nicotinic subunits in autonomic ganglia includes alpha3, alpha5, alpha7, beta2 and beta4 subunits. In the last 10 years, heterologous expression studies have revealed much about the nature of neuronal nAChRs. However, there is only limited understanding of subunit actions in autonomic system. Functional deletions of subunit by gene knockout in animals could overcome these limitations. We review recent studies on nAChRs on autonomic ganglia for physiological and pharmacological properties and potential locations of the subunits.

Nicotinic receptor-mediated effects on appetite and food intake

It is well known, although not well understood, that smoking and eating just do not go together. Smoking is associated with decreased food intake and lower body weight. Nicotine, administered either by smoking or by smokeless routes, is considered the major appetite-suppressing component of tobacco. Perhaps the most renowned example of nicotine's influence on appetite and feeding behavior is the significant weight gain associated with smoking cessation. This article presents an overview of the literature at, or near, the interface of nicotinic receptors and appetite regulation. We first consider some of the possible sites of nicotine's action along the complex network of neural and non-neural regulators of feeding. We then present the hypothesis that the lateral hypothalamus is a particularly important locus of the anorectic effects of nicotine. Finally, we discuss the potential role of endogenous cholinergic systems in motivational feeding, focusing on cholinergic pathways in the lateral hypothalamus.

Lower urinary tract physiology and pharmacology

This review focuses on what we consider to be the most important findings of the last year relating to the smooth muscle of the lower urogenital system and the different levels of regulation that control its contraction and relaxation. One level is through modulation of the smooth muscle itself or its environment. Recent findings examining myosin isoform composition and collagen content as well as mechanisms that appear to be involved in inducing hyperplasia/hypertrophy of smooth muscle are described. Another method of regulation is via calcium-dependent phosphorylation of the regulatory light chain of myosin, which increases its activity. Interesting results indicating an uncoupling of force from calcium in the bladder are discussed. A third level of regulation is pharmacologic. Thus, the most recent findings related to receptor subtypes, including muscarinic, endothelin, alpha-adrenergic and nicotinic receptors, are presented. In addition, the effects of diabetes, incontinence, and partial bladder outlet obstruction on these modes of contractile regulation are also discussed.