Stimulation of adrenergic nerve fibres to the urinary bladder of the rat

Acute bladder decentralization in hound dogs: Preliminary results of effects on hypogastric nerve electroneurograms and detrusor pressure responses to spinal root and hypogastric nerve stimulation

OBJECTIVE

We aimed to refine electroneurogram techniques for monitoring hypogastric nerve activity during bladder filling, and then examined nerve activity in normal intact versus acutely decentralized bladders.

METHODS

Effects of electrical stimulation of hypogastric nerves or lumbar ventral roots on detrusor pressure were examined, as were effects of isoflurane versus propofol anesthetics on hypogastric nerve stimulation evoked pressure. Hypogastric nerve activity was then recorded using custom-made bipolar cuff electrodes during bladder filling before and after its transection between the spinal cord and electrode to eliminate efferent nerve signals.

RESULTS

Electrical stimulation of hypogastric nerves evoked low amplitude detrusor pressures that did not differ between the two anesthetics. Upper lumbar (L2) ventral root stimulation evoked detrusor pressures were suppressed, yet not eliminated, after transection of hypogastric nerves and all spinal roots below L5. Afferent and efferent hypogastric nerve activity did not change with bladder filling in neuronally intact bladders yet decreased in decentralized bladders. No change in afferent activity was observed during bladder filling in either intact or decentralized bladders.

CONCLUSIONS

These findings indicate that a more complete decentralized bladder model should include transection of lumbosacral spinal roots innervating the bladder as well as hypogastric nerves. These refined electroneurogram recording methods may be suitable for evaluating the effectiveness of nerve transfer surgeries for bladder reinnervation by monitoring sensory activity in the transferred nerve.

Autonomic control of the urogenital tract

The urogenital tract houses many of the organs that play a major role in homeostasis, in particular those that control water and salt balance, and reproductive function. This review focuses on the anatomical and functional innervation of the kidneys, urinary ducts and bladders of the urinary system, and the gonads, gonadal ducts, and intromittent organs of the reproductive tract. The literature, especially in recent years, is overwhelmingly skewed toward the situation in mammals. Nevertheless, where specific neurochemical markers have been investigated, common patterns of innervation can be found in representatives from most vertebrate classes. Not surprisingly the vasculature, epithelia and smooth muscle of all urogenital organs receives adrenergic innervation. These nerves may contain non-adrenergic non-cholinergic (NANC) neurotransmitters such as ATP and NPY. Cholinergic nerves increase motility in most urogenital organs with the exception of the kidney. The major NANC nerves found to influence urogenital organs include those containing VIP/PACAP, galanin and neuronal nitric oxide synthase. These can be found associated with both smooth muscle and epithelia. The role these nerves play, and the circumstances where they are activated are for the most part unknown.

Cholinergic mechanisms in the rat detrusor muscle

The motor response of the urinary bladder to nerve stimulation is resistant to atropine, and it has been proposed that the nerves are non-cholinergic, but are possibly purinergic. In this review evidence is presented suggesting a cholinergic transmission in the rat detrusor muscle, part of the receptors being inaccessible to atropine. The rat bladder receives postganglionic cholinergic fibres not only from the pelvic but also from the hypogastric nerves, some fibres passing outside the pelvic ganglia and some relaying distal to them. There is a functional overlap between the right and the left pelvic nerve, but the contractile response to stimulation of the hypogastric nerves is added to the pelvic nerve response with no functional overlap or antagonism.

M1 muscarinic receptor-induced facilitation of ACh and noradrenaline release in the rat bladder is mediated by protein kinase C

1. [3H]Noradrenaline (NA) AND [14C]acetylcholine (ACh) released by electrical field stimulation were measured simultaneously in strips from the body of rat urinary bladder. 2. [3H]NA and [14C]ACh release was greater during continuous stimulation (CS; 10 Hz, 100 shocks) or in the presence of eserine than during intermittent train stimulation (IS; 10 Hz, 10 shocks every 5 s, 10 times). Atropine (1 microM) or pirenzepine (0.05-0.1 microM) blocked the CS- or eserine-facilitated release. 3. The protein kinase C (PKC) activator phorbol dibutyrate (PDB; 0.05 and 0.5 microM) increased the release of both [3H]NA and [14C]ACh in a concentration-dependent manner. Atropine blocked the PDB-induced facilitation of ACh release but not the facilitation of NA release. 4. The protein kinase A (PKA) activator 8-Br-cAMP did not affect ACh release but enhanced NA release. 5. The PKC inhibitor H-7 (50-100 microM) inhibited the CS- or eserine-facilitated release of both ACh and NA, but did not affect the non-facilitated release evoked by IS. H-7 also inhibited 0.5 microM PDB-induced facilitation of ACh release but not NA release. 6. Down-regulating PKC by pretreatment for 30 min with 5 microM PDB decreased the facilitated release of ACh and the eserine-induced facilitation of NA release. 7. Electrically evoked contractions of the bladder strips exhibited a biphasic response to PDB (2.5 microM), which consisted of an initial enhancement of the peak amplitude and area followed after 20 min by an inhibition of contractions. H-7 inhibited the electrically evoked contractions in a dose-dependent fashion. 8. It is concluded that a phospholipase C-PKC signal transduction pathway is essential for muscarinic receptor-induced facilitation of ACh and NA release but is not involved in the non-facilitated release of transmitters in the rat urinary bladder.

Urinary bladder innervation in children

Muscle strips from the fundus, trigone, and distal ureter obtained from children at operation for vesicoureteric reflux were studied using histochemical and immunohistochemical methods, and electrical nerve stimulation in an organ bath. A rich supply of cholinergic nerves was found and the transmitter causing contraction of the detrusor muscle was regarded as being acetylcholine. The adrenergic innervation was very sparse except around the ureteric orifices. No contractile alpha-adrenoceptors could be detected but beta-receptor-mediated relaxation was found. The type was not beta 1 or beta 2, suggesting a third type of beta-receptor. Peptidergic nerves containing vasoactive intestinal peptide (VIP) were demonstrated in a few nerve terminals. No nerves containing enkephalin, somatostatin, or substance P were found. VIP affected the detrusor muscle, indicating a possible role as a modulator of transmitter action. Imipramine, used for enuresis, had no anticholinergic effect on the bladder in the doses used clinically. The anticholinergic and calcium antagonistic drug terodiline inhibited all muscle activity, making it suitable for treatment of diurnal enuresis.

Innervation of the child urinary bladder

Muscle strips from the fundus, trigonum and distal ureters obtained from children at operations for vesico-ureteric reflux were studied using histochemical and immunohistochemical methods, and electrical nerve stimulation in an organ bath. A rich supply of cholinergic nerves was found and despite a partial atropine resistance the neurophysiological experiments indicated that the transmitter causing contraction of the detrusor muscle is acetylcholine. Imipramine, which is used in the treatment of enuresis, had no anticholinergic effect on the bladder in the doses used clinically. The adrenergic innervation was very sparse except around the ureter orifices. No contractile alpha-adrenoceptors could be detected but beta receptor mediated relaxation was found, which was neither of the beta 1 nor beta 2 type. A third type of beta receptor is postulated. Peptidergic nerves containing vasoactive intestinal peptide, VIP, were demonstrated in a few nerve terminals running along bundles of smooth muscle. No nerves containing enkephaline, somatostatine or substance P were found. VIP affected the detrusor muscle indicating a possible role as a modulator of transmitter action, while substance P had no effect. The anticholinergic and calcium antagonistic drug terodiline inhibited all muscle activity, whether it was induced by nerve stimulation, cholinergic drugs or a potassium rich solution, making it suitable for treatment of diurnal enuresis.

Interaction of tachykinins with an adrenergic receptor in the rat urinary bladder

The rat urinary bladder was examined as a model for studying tachykinin receptors. The order of potency, the maximal effect and the slope of the dose-response curve were examined with six tachykinins - substance P (SP), physalaemin, phyllomedusin, uperolein, eledoisin, kassinin - and several substance P fragments - SP-(2-11), SP-(3-11), SP-(4-11) and SP-(6-11). The tachykinin receptor on the rat urinary bladder was shown to bind preferentially tachykinins having a hydrophilic amino acid residue in position 5-6, as occurs with physalaemin, phyllomedusin, eledoisin and kassinin. The N-terminal of the tachykinins and in particular substance P is suggested to play a major role in regulating affinity, intrinsic activity and the slope of the dose-response curve. The tachykinins are thought to exert a direct action on smooth muscle. An accessory binding site associated with the tachykinin receptor on rat urinary bladder was also identified. This accessory site binds the N-terminal amino acids of the tachykinins as well as some alpha-adrenergic compounds (phentolamine, prazosin, noradrenaline or adrenaline in the presence of propranolol). When the accessory binding site is occupied by adrenergic compounds, the affinity of the tachykinins is markedly reduced. This observation is interpreted to mean that catecholamines may have a modulatory influence on tachykinin activity on the rat urinary bladder.

Comments on the atropine resistance of the neurogenic contractile response of the rat detrusor muscle

The resistance to atropine or scopolamine of the neurogenic contractile response to field stimulation of intramural nerves of the rat detrusor was studied during the early phase of Wallerian degeneration in vitro and in vivo. The neurogenic contractile response to low frequency stimulation of control bladders was completely resistant to atropine or scopolamine in vitro. As a matter of fact the response was enchanced by the drugs. In vivo a transient shortening of the response could be seen. 26-34 h after bilateral extirpation of the pelvic ganglia there was prominent degeneration activity in the bladders in vitro as well as in vivo. Atropine or scopolamine inhibited this activity in vivo but enhanced it in vitro. The neurogenic contractile response to field stimulation of the bladder nerves was blocked in vivo but not in vitro by the antimuscarinic drugs 26-34 h after neurectomy. The results support the concept that the excitatory neurotransmission in the detrusor is essentially cholinergic. An explanation of the difference between the in vivo and the in vitro results based on differences in degree of blockade of pre- and post-junctional muscarinic receptors and diffusion of the antimuscarinics in the tissue is proposed.

Increase in choline acetyltransferase activity in surgically isolated postganglionic parasympathetic neurones of the urinary bladder of adult rats

In the urinary bladder of adult male rats the choline acetyltransferase activity in postganglionic neurones isolated from the central nervous system was shown to increase markedly and rapidly following section of the contralateral postganglionic neurones. The enzyme activity of the operated bladder was 32% of the control 3 days postoperatively, while at the last observation, 25 days postoperatively, it was 86%. As judged from additional studies on totally denervated bladders and on totally decentralized bladders the increase found in the enzyme activity was not due to ingrowth of nerves from outside or to unspecific acetylcholine synthesis neither was it due to increase in bladder wall tension or to increase in tissue mass.

Compensatory increase of responses to nerve stimulation of the partially denervated rat urinary bladder

The rat urinary bladder was deprived of half of its innervation by removing the pelvic ganglion on one side. The motor response of such a partially denervated bladder to stimulation of the pelvic nerve on the other side were examined 1 week, 1 month and 2 months postoperatively. On all three occasions the increase in pressure of the operated bladder was larger than that of the control bladder; the enlargement was most marked 2 months after operation. The responses were further enlarged by eserine, and markedly reduced by atropine. The present results combined with those of previous investigations, showing a rapid recovery in the activity of the acetylcholine forming enzyme from a reduced level and a transient supersensitivity to chemical stimuli after unilateral removal of the pelvic ganglion, suggest that the enlarged responses to nerve stimulation 1 week postoperatively are mainly due to sensitization, while those observed at the later stages are due to collateral sprouting from the cholinergic nerve fibres of the intact pelvic nerve.

Adrenergic reinnervation of the denervated rat urinary bladder

In rats undergoing unilateral extirpation of the pelvic ganglion, the adrenergic innervation disappeared on the ipsilateral side of the urinary bladder. It had reappeared after 6--9 weeks.

Choline acetyltransferase activity in the denervated urinary bladder of the rat

After extirpation of the pelvic ganglia the choline acetyltransferase activity decreased markedly indicating that most of the postganglionic cholinergic neurones of the bladder take this route. A small decrease in the activity of this enzyme was found after section of the hypogastric nerve, showing that these nerves contribute to some extent to the cholinergic innervation. The residual enzyme activity found after a combination of the two surgical procedures suggests that neurones relay distal to the level of the section of the hypogastric nerves and pass outside the pelvic ganglia and (or) that neurones pass the pelvic ganglia and relay distal to them. Electrical stimualtion of the hypogastric nerves after extirpation of the pelvic ganglia and the use of blocking drugs showed on the existence of cholinergic neurones passing outside the pelvic ganglia, some of them relaying distal to the point of stimulation.

Responses of the denervated rat urinary bladder to alfa adrenoceptor stimulation

The contractile responses of the rat detrusor muscle to noradrenaline were increased 2-3 weeks after partial denervation but had returned to control values 6-9 weeks after the denervation, probably because of reinnervation of denervated muscle cells. 6-9 weeks after partial denervation the excitatory alpha-adrenoceptor mediated response to stimulation of the remaining intact nerves was predominant, masking the subsequent inhibitory beta-receptor response, which at this time was seen only after alpha-receptor blockade. The possibility of an outgrowth of adrenergic fibres activating alpha-receptors in muscle cells normally not innervated by adrenergic nerves is discussed.