Effects Of Field Stimulation Research Articles

The functional and structural response to distention of the rabbit whole bladder in vitro.

We investigated the effects of distention on intravesical pressure generation in response to stimuli in relation to its effects on bladder wall thickness and morphology. A total of 25 New Zealand White rabbits were separated into 5 groups of 5 each. Each in vitro whole bladder preparation was filled with saline to 5% (undistended), 25%, 50%, 100% or 125% capacity (60 ml.). The effects of field stimulation, adenosine 5'-triphosphate, carbamylcholine chloride (carbachol) and KCl on intravesical pressure generation were determined. Additional bladders were similarly distended (3 at each percent of capacity), fixed in formalin and evaluated by semiquantitative morphometry. Pressure generation in response to field stimulation was maximal at 5% of capacity and it decreased progressively thereafter. Compared with the responses of undistended bladders, at 25% capacity the response to carbachol increased and then decreased progressively above 25%. Distention had no significant effect on the response to KCl. Interestingly pressure generation in response to adenosine 5'-triphosphate was increased more than 4-fold at 25% bladder capacity compared with 5% and it did not change significantly thereafter. Bladder wall thickness was decreased more than 50% at 25% capacity and by an additional 12% at 125% capacity. The greatest thinning was observed in the mucosa compared with the submucosa and muscularis. Bladder distention significantly reduced pressure generation in response to field stimulation only, indicating that distention reduced the effectiveness of synaptic transmission without altering muscarinic receptor function or membrane depolarization. The greatest change (decrease) in the response to field stimulation occurred between 5% (undistended) and 25% capacity, which was the change in distention that most affected bladder wall thinning.

The Functional and Structural Response to Distention of the Rabbit Whole Bladder In Vitro

We investigated the effects of distention on intravesical pressure generation in response to stimuli in relation to its effects on bladder wall thickness and morphology. A total of 25 New Zealand White rabbits were separated into 5 groups of 5 each. Each in vitro whole bladder preparation was filled with saline to 5% (undistended), 25%, 50%, 100% or 125% capacity (60 ml.). The effects of field stimulation, adenosine 5'-triphosphate, carbamylcholine chloride (carbachol) and KCl on intravesical pressure generation were determined. Additional bladders were similarly distended (3 at each percent of capacity), fixed in formalin and evaluated by semiquantitative morphometry. Pressure generation in response to field stimulation was maximal at 5% of capacity and it decreased progressively thereafter. Compared with the responses of undistended bladders, at 25% capacity the response to carbachol increased and then decreased progressively above 25%. Distention had no significant effect on the response to KCl. Interestingly pressure generation in response to adenosine 5'-triphosphate was increased more than 4-fold at 25% bladder capacity compared with 5% and it did not change significantly thereafter. Bladder wall thickness was decreased more than 50% at 25% capacity and by an additional 12% at 125% capacity. The greatest thinning was observed in the mucosa compared with the submucosa and muscularis. Bladder distention significantly reduced pressure generation in response to field stimulation only, indicating that distention reduced the effectiveness of synaptic transmission without altering muscarinic receptor function or membrane depolarization. The greatest change (decrease) in the response to field stimulation occurred between 5% (undistended) and 25% capacity, which was the change in distention that most affected bladder wall thinning.

The effects of field stimulation on bovine mesenteric lymph node contractility

In these studies isometric tension was recorded from isolated strips of bovine mesenteric lymph node capsule. The possible influence of intrinsic nerves on their contractile activity was examined using field stimulation and the pharmacology of the response was investigated. Over 75% of the tissues studied demonstrated regular spontaneous activity at a frequency of 3.9 +/- 0.2 contractions/5 min under control conditions. Field stimulation at 2.8 and 32 Hz (pulse width = 0.3 ms, nominal voltage 60 V) produced frequency-dependent increases in the rate of this spontaneous activity associated with a raised baseline tension. These responses were not diminished on repeat stimulation under control conditions. The contraction frequency response to stimulation at 8 Hz was blocked completely in the presence of 1 microM tetrodotoxin, while the increase in baseline tension was reduced by over 80%, suggesting that field stimulation was activating intrinsic nerves. The responses to stimulation (8 Hz) were also greatly reduced by 10 microM phentolamine but were unaffected by 10 microM propranolol. These experiments suggest that intrinsic nerves can modulate the contractile activity of lymph node capsule acting, at least in part, through excitatory alpha-adrenoceptors. The possible functional significance of this is discussed.

Intrathyroidal autonomic nerves can directly influence hormone release from rat thyroid follicles: a study in vitro employing electrical field stimulation and intracellular microelectrodes.

The role of the autonomic nervous system in the control of thyroxine release from the rat thyroid gland in vitro, has been investigated using electrical field stimulation as a device to induce intrathyroidal nerves to release their neurotransmitters. The effects of field stimulation on follicular cell membrane potential and input resistance have been investigated using continuous intracellular recordings from individual cells. Electrical field stimulation promotes up to an eightfold increase in throxine release from the thyroid gland in vitro. This effect is blocked by the neurotoxin, tetrodotoxin. Electrical field stimulation has no effect on follicular cell membrane potential or input resistance. This is consistent with the results of previous pharmacological experiments using this preparation. It is concluded that electrical field stimulation induces intrathyroidal nerves to release their neurotransmitters, and that the net effect of this is to cause thyroxine release from the thyroid follicles. The existence of a directly acting secretomotor innervation to the thyroid follicle is suggested.

Adrenergic excitatory and cholinergic inhibitory innervations in the human iris dilator

To investigate the pattern of innervation in the human iris dilator muscle, effects of field stimulation on the isometric tension of dilator muscle were investigated in vitro. Throughout the experiments, spontaneous contractions did not occur. Application of repetitive field stimulations evoked biphasic mechanical responses (i.e. an initial phasic contraction followed by long lasting relaxation) of the isolated human iris dilator. These mechanical responses were abolished by 10 −7 m tetrodotoxin (a nerve poison), thereby indicating that the mechanical responses were neurogenic. Furthermore, the initial phasic contractions and following muscle relaxation were selectively blocked by phentolamine (10 −5 m) and atropine (10 −5 m), respectively. The degree of the muscle relaxation to that of contraction was much larger than that assumed by other investigators who used tissues from different species. The present results indicate that the human iris dilator muscle is innervated by adrenergic excitatory and cholinergic inhibitory nerves, and that cholinergic inhibitory innervations in this muscle may support the cholinergic miosis in the iris sphincter muscle.

Neuropeptide action on the guinea-pig bladder; a comparison with the effects of field stimulation and ATP

A comparison was made between the effects of several neuropeptides and ATP as possible mediators of the non-adrenergic, non-cholinergic excitatory response in detrusor strips from the guinea-pig urinary bladder. Both substance P and vasoactive intestinal polypeptide produced contractions of the guinea-pig bladder, but the form of the atropine-resistant neurogenic excitation was mimicked more precisely by ATP. Neither methionine enkephalin nor leucine enkephalin had a prominent direct action on the smooth muscle (up to 100 μM) and did not significantly modify the cholinergic or non-cholinergic components of the response elicited by field stimulation. A proteolytic enzyme, chymotrypsin (10 U/ml), antagonised the excitatory effect of substance P, but not that of the non-adrenergic, non-cholinergic excitatory response or ATP. The slow excitation elicited by a high concentration of vasoactive intestinal polypeptide (10 μM), in contrast to responses elicited by ATP or field stimulation, was attenuated by preincubation with the structurally related polypeptide PHI, which was itself inactive (up to 10 μM). The present observations argue against a role for the peptides studied as neuromuscular transmitters in the detrusor but do not preclude such a role for ATP.

Substance P is a functional neurotransmitter in the rat parotid gland.

The technique of electrical field stimulation was employed to stimulate the intrinsic nerves of isolated rat parotid gland fragments. Responses to field stimulation were recorded as changes in enzyme secretion (amylase release), radiolabelled ion fluxes (86Rb efflux) and electrophysiological effects (changes in acinar cell membrane potential and input resistance). All effects of field stimulation were abolished by the neurotoxin, tetrodotoxin (TTX). Selective use of pharmacological antagonists revealed that both the sympathetic and parasympathetic nerves to this tissue were being excited by field stimulation. Importantly a significant component of the response to field stimulation persisted in the presence of combined autonomic receptor blockade by atropine, phentolamine and propranolol, i.e. due to release of a non-cholinergic, non-adrenergic neurotransmitter. The non-cholinergic, non-adrenergic neurotransmitter evoked amylase release, 86Rb efflux and electrophysiological effects seen as changes in acinar cell membrane potential and conductance, i.e. stimulus-permeability coupled. Two biologically active peptides, substance P (SP) and vasoactive intestinal polypeptide (VIP) were shown to evoke amylase release in the presence of combined autonomic blockade. VIP however did not evoke any increase in 86Rb efflux, i.e. not stimulus-permeability coupled. All the effects of the non-cholinergic, non-adrenergic transmitter were mimicked by substance P which evokes 86Rb efflux and electrophysiological effects in addition to amylase release. The non-cholinergic, non-adrenergic field stimulus effects on amylase release and 86Rb efflux were abolished or markedly attenuated in tissues which had been desensitized by prior exposure to exogenous substance P. In the presence of VIP, however, the non-cholinergic, non-adrenergic effects persisted and were apparently potentiated. Acute application of the neurotoxin capsaicin first stimulated a transient release of amylase and subsequently abolished the non-cholinergic, non-adrenergic field stimulus-evoked enzyme release. The putative substance P antagonist, D-Pro2, D-Trp7,9 substance P, reversibly blocked the response to both non-cholinergic, non-adrenergic nerve stimulation and exogenous substance P. It was demonstrated however that prolonged exposure to this antagonist is associated with non-reversible and, importantly, non-specific neurotoxic effects. It is concluded that substance P or a closely related peptide is a functional neurotransmitter in the rat parotid gland.

Effects of field stimulation on submucosal plexus in the isolated guinea pig ureter.

In a preparation consisting of the reversed ureter of the guinea pig, by field stimulation action potentials originating from nerve fibers and smooth muscle cells were recorded. The smooth muscle action potential was assumed to be due to excitation of the nerve fibers.

Effects of field stimulation on cholinergic fibers of the pelvic region in the isolated guinea pig ureter.

Electrical activities have been recorded in a preparation consisting of the pelvic region and the upper ureter of the guinea pig. Train field stimulation of the pelvic region evoked a train of nerve action potentials followed by a multiphasic smooth muscle action potential after a latency of about 2.5--8.0 sec. This smooth muscle response was abolished by tetrodotoxin and dibucaine, and also by cholinergic blocking agents. The response was furthermore, inhibited by decreasing Ca/4 concentration and increasing Mg/+ concentration in Tyrode solution. This is therefore considered to be the response synaptically evoked by cholinergic fibers in the pelvic region. Mechanical activities have been investigated on the same preparations by the Magnus method. Acetylcholine (10(-7)--10(-4) g/ml) produced a group of twitch responses which were antagonized by cholinergic blocking agents. The responsiveness of the preparations to acetylcholine was markedly decreased by removal of the pelvic region. Cholinesterase activities in the calyx-pelvis and upper ureter have been estimated by the biochemical method. A preparation consisting of calyx-pelvis exhibited twice the enzyme activity as compared with the upper ureter. These results suggesteds that there is a cholinergic innervation in the pelvic region of the guinea pig ureter which also takes part in control of the ureteric activity.

Some electrical properties of the rabbit anococcygeus muscle and a comparison of the effects of inhibitory nerve stimulation in the rat and rabbit.

1. Simultaneous recordings of mechanical activity and membrane potential of individual smooth muscle cells have been made in the rabbit anococcygeus muscle and the effect of field stimulation on these examined.2. In the absence of tone the mean resting membrane potential was - 48 mV. In the stretched muscle spontaneous tone and rhythmic activity quite frequently appeared and this was associated with depolarization of the muscle cells.3. The response to field stimulation depended on the frequency of stimulation, the level of membrane potential and the presence of myogenic tone. The usual response to single pulses or low frequency stimulation was a hyperpolarization of up to 30 mV (mean 14+/-6.8 mV) after a latency of 185 msec and accompanied by muscle relaxation. Higher frequencies (over 8 Hz) produced an initial depolarization often with a spike potential and followed by hyperpolarization. The mechanical response in these instances was contraction or contraction followed by relaxation. At all frequencies rebound depolarization and an associated contraction followed the end of stimulation).4. Phentolamine (5x10(-6)M) and guanethidine (10(-6)M) blocked the initial depolarization and contraction but had no effect on hyperpolarization, muscle relaxation or rebound depolarization and contraction.5. The effect of field stimulation in the presence of guanethidine (4x10(-5)M) was re-examined in the rat anococcygeus. Single pulses were ineffective, repetitive stimulation produced muscle relaxation but no hyperpolarization comparable to the rabbit. Any oscillations in membrane potential were damped during field stimulation and sometimes a small hyperpolarization was produced with a maximum amplitude of 13 mV and a mean of 1.9+/-1.2 mV.6. The transmembrane potential at the peak of hyperpolarization in the rabbit was rarely more than -70 mV. Passive displacement of the membrane potential by current pulses altered the amplitude of the hyperpolarization and suggested that there was a reversal potential at between -80 and -90 mV.7. No change in input resistance could be measured during inhibitory nerve stimulation in either the rabbit or the rat but measurements based on electrotonic potentials indicated a reducation in membrane resistance, small in the rat but greater in the rabbit.8. These experiments suggest that in both species muscle relaxation is associated with an increase in ionic permeability and a move, at least in the rabbit muscle, towards an equilibrium potential of -80 to -90 mV. In view of the much smaller effect in the rat it is not clear whether this is the cause or at least the sole cause of the muscle relaxation.

Effects of Field Stimulation on Nerve Terminals in Human Blood Vessels.

Noradrenaline and dopamine ß-hydroxylase normally appear to be released from the nerve terminal by exocytosis and data from several laboratories indicate that, during severe stress, a close correlation exists between the level of these substances in the plasma and sympathetic activity. Ultrastructural evidence for exocytosis at the noradrenergic terminal in humans is lacking and it is not known if the large vesicle (LV) or small vesicle (SV) type, or both, are involved in the release process. The present study was performed to find morphological evidence of exocytosis.Portions of omental arteries and veins were obtained from patients undergoing abdominal surgery using routine general anesthesia. Control vessels were placed in fixative within 10-30 sec after excision, or they were treated similarly to experimental vessels except that field stimulation was omitted prior to fixation.