Prostaglandins and neurotransmission at the guinea pig and rabbit urinary bladder

Prostaglandin E2 excitatory effects on guinea pig urinary bladder smooth muscle: a novel regulatory mechanism mediated by large-conductance voltage- and Ca2+-activated K+ channels

Prostaglandin E2 (PGE2) is an essential signaling molecule involved in the regulation of detrusor smooth muscle (DSM) function. However, the underlying regulatory mechanism by which PGE2 augments DSM cell excitability and contractility is not well understood. Here, we investigated whether PGE2 inhibits the large conductance voltage- and Ca(2+)-activated K(+) (BK) channels in guinea pig DSM, thereby increasing DSM excitability and contractility. We used a multidisciplinary experimental approach including amphotericin-B perforated patch-clamp electrophysiology and live-cell Ca(2+) imaging in native freshly-isolated DSM cells, isometric tension recordings of intact DSM strips, and pharmacological tools to investigate BK channel regulation by PGE2 in guinea pig DSM. PGE2 increased the spontaneous phasic contractions of isolated DSM strips in a concentration-dependent manner (10 nM-10 µM). BK channel inhibition with paxilline (1 µM) attenuated the PGE2-induced DSM phasic contractions, suggesting that BK channels are involved in the mechanism of PGE2-induced DSM contractions. PGE2 (10 µM) increased the intracellular Ca(2+) levels in freshly-isolated DSM cells. PGE2 (10 µM) also caused an inhibition of the amplitude and frequency of spontaneous transient BK currents in DSM cells. Moreover, PGE2 (10 µM) did not affect the amplitude of whole cell steady-state BK currents in DSM cells. Our findings provide strong experimental evidence that PGE2 leads to an inhibition of the spontaneous transient BK currents, elevation of intracellular Ca(2+) levels in freshly-isolated DSM cells, and augmentation of DSM phasic contractions. Thus, we have revealed a novel mechanism that BK channels mediate PGE2-induced contractions in guinea pig DSM.

Enhancement effects of nicotine on neurogenic contractile responses in rabbit gastric fundus

Nicotine, a nicotinic acetylcholine receptor agonist, plays a role in the modulation of neurotransmitter release following nerve stimulation in both the central and the peripheral nervous system. Nitric oxide and prostaglandins modulate the release of various neurotransmitters in different tissues. We aimed to investigate the effects of nicotine on neurogenic contractile responses via nicotinic acetylcholine receptors and, if a change occurred, to investigate the effects of N(W)-nitro-L-arginine methyl ester (L-NAME) and indomethacin on this change in rabbit gastric fundus. Electrical field stimulation (EFS)-evoked contractile responses were recorded from gastric fundus strips obtained from rabbits with an isometric force displacement transducer. Nicotine was applied to preparations at varying concentrations. Then, the effects of hexamethonium, cadmium (Cd(2+)), indomethacin, and L-NAME were tested on the EFS-evoked contractions in the presence of nicotine. Nicotine-induced transient neurogenic contractions in a dose-dependent manner. Cd(2+) and hexamethonium inhibited nicotine-induced transient neurogenic contractions, but indomethacin and L-NAME produced no effect. In conclusion, nicotine increased EFS-evoked contractile responses, possibly by facilitating neurotransmitter release from nerve terminals by a mechanism dependent on the influx of Ca(2+) from voltage-gated Ca(2+) channels via activation of nicotinic acetylcholine receptors in isolated rabbit gastric fundus. Endogenous nitric oxide and prostaglandins do not play a physiological role in the regulation of this neurotransmitter release.

Nicotine potentiates the neurogenic contractile response of rabbit bladder tissue via nicotinic acetylcholine receptors: Nitric oxide and prostaglandins have no role in this process

Nicotine, a nicotinic acetylcholine receptors (nAChRs) agonist, has a role in modulation of the neurotransmitter release following nerve stimulation in both the central and peripheral nervous systems. The aim of this study was to determine whether electrical field stimulation (EFS)-evoked contractions are altered in rabbit bladder in the presence of nicotine and, if an alteration occurs, to investigate the effects of nitric oxide and prostaglandins on nicotine-induced alternation in isolated rabbit bladder. EFS-evoked contractile responses from rabbit bladder obtained were recorded with isometric force displacement transducers. Nicotine was added to preparations at various concentrations. The effects of hexamethonium, cadmium (Cd(2+)), indomethacin and N-nitro-L-arginine methyl ester (L-NAME) were tested on the EFS-evoked contractions in the presence of nicotine. Nicotine led to a dose-dependent increase in the amplitude of the EFS-evoked contractile responses. Cd(2+) and hexamethonium inhibited the nicotine-induced increase in EFS-evoked responses, whereas indomethacin and L-NAME had no effect. In conclusion, nicotine increased the EFS-evoked contractile responses possibly by facilitating release of neurotransmitters from nerve terminals by a mechanism dependent on the influx of Ca(2+) from voltage-gated Ca(2+) channels (VGCCs) via activation of nAChRs in isolated rabbit bladder. Nitric oxide and prostaglandins do not have a physiological role in the regulation of neurotransmitter release.

Pharmacology of the lower urinary tract: basis for current and future treatments of urinary incontinence

The lower urinary tract constitutes a functional unit controlled by a complex interplay between the central and peripheral nervous systems and local regulatory factors. In the adult, micturition is controlled by a spinobulbospinal reflex, which is under suprapontine control. Several central nervous system transmitters can modulate voiding, as well as, potentially, drugs affecting voiding; for example, noradrenaline, GABA, or dopamine receptors and mechanisms may be therapeutically useful. Peripherally, lower urinary tract function is dependent on the concerted action of the smooth and striated muscles of the urinary bladder, urethra, and periurethral region. Various neurotransmitters, including acetylcholine, noradrenaline, adenosine triphosphate, nitric oxide, and neuropeptides, have been implicated in this neural regulation. Muscarinic receptors mediate normal bladder contraction as well as at least the main part of contraction in the overactive bladder. Disorders of micturition can roughly be classified as disturbances of storage or disturbances of emptying. Failure to store urine may lead to various forms of incontinence, the main forms of which are urge and stress incontinence. The etiology and pathophysiology of these disorders remain incompletely known, which is reflected in the fact that current drug treatment includes a relatively small number of more or less well-documented alternatives. Antimuscarinics are the main-stay of pharmacological treatment of the overactive bladder syndrome, which is characterized by urgency, frequency, and urge incontinence. Accepted drug treatments of stress incontinence are currently scarce, but new alternatives are emerging. New targets for control of micturition are being defined, but further research is needed to advance the pharmacological treatment of micturition disorders.

Urinary bladder contraction and relaxation: physiology and pathophysiology

The detrusor smooth muscle is the main muscle component of the urinary bladder wall. Its ability to contract over a large length interval and to relax determines the bladder function during filling and micturition. These processes are regulated by several external nervous and hormonal control systems, and the detrusor contains multiple receptors and signaling pathways. Functional changes of the detrusor can be found in several clinically important conditions, e.g., lower urinary tract symptoms (LUTS) and bladder outlet obstruction. The aim of this review is to summarize and synthesize basic information and recent advances in the understanding of the properties of the detrusor smooth muscle, its contractile system, cellular signaling, membrane properties, and cellular receptors. Alterations in these systems in pathological conditions of the bladder wall are described, and some areas for future research are suggested.

Electrophysiological evidence of intuition: part 1. The surprising role of the heart

OBJECTIVES

This study aims to contribute to a scientific understanding of intuition, a process by which information normally outside the range of conscious awareness is perceived by the psychophysiological systems. The first objective, presented in two empirical papers (Part 1 and Part 2), was to replicate and extend the results of previous experiments demonstrating that the body can respond to an emotionally arousing stimulus seconds before it is actually experienced. The second objective, to be presented in a third paper (Part 3), is to develop a theory that explains how the body receives and processes information involved in intuitive perception.

DESIGN

The study used a counterbalanced crossover design, in which 30 calm and 15 emotionally arousing pictures were presented to 26 participants under two experimental conditions: a baseline condition of normal psychophysiologic function and a condition of physiological coherence. Primary measures included: skin conductance; the electroencephalogram (EEG), from which cortical event-related potentials and heartbeat-evoked potentials were derived; and the electrocardiogram (ECG), from which cardiac decelerations/accelerations were derived. These measures were used to investigate where and when in the brain and body intuitive information is processed.

RESULTS

The study's results are presented in two parts. The main findings in relation to the heart's role in intuitive perception presented here are: (1) surprisingly, the heart appears to receive and respond to intuitive information; (2) a significantly greater heart rate deceleration occurred prior to future emotional stimuli compared to calm stimuli; (3) there were significant gender differences in the processing of prestimulus information. Part 2 will present results indicating where in the brain intuitive information is processed and data showing that prestimulus information from the heart is communicated to the brain. It also presents evidence that females are more attuned to intuitive information from the heart.

CONCLUSIONS

Overall, we have independently replicated and extended previous research documenting prestimulus responses. It appears that the heart is involved in the processing and decoding of intuitive information. Once the prestimulus information is received in the psychophysiologic systems, it appears to be processed in the same way as conventional sensory input. This study presents compelling evidence that the body's perceptual apparatus is continuously scanning the future. To account for the results presented in Parts 1 and 2, Part 3 will develop a theory based on holographic principles explaining how intuitive perception accesses a field of energy into which information about future events is spectrally enfolded.