Localization of muscarinic receptors on somatostatin-like immunoreactive neurones of the newborn guinea pig urinary bladder in culture

Neural control of the lower urinary tract

This article summarizes anatomical, neurophysiological, pharmacological, and brain imaging studies in humans and animals that have provided insights into the neural circuitry and neurotransmitter mechanisms controlling the lower urinary tract. The functions of the lower urinary tract to store and periodically eliminate urine are regulated by a complex neural control system in the brain, spinal cord, and peripheral autonomic ganglia that coordinates the activity of smooth and striated muscles of the bladder and urethral outlet. The neural control of micturition is organized as a hierarchical system in which spinal storage mechanisms are in turn regulated by circuitry in the rostral brain stem that initiates reflex voiding. Input from the forebrain triggers voluntary voiding by modulating the brain stem circuitry. Many neural circuits controlling the lower urinary tract exhibit switch-like patterns of activity that turn on and off in an all-or-none manner. The major component of the micturition switching circuit is a spinobulbospinal parasympathetic reflex pathway that has essential connections in the periaqueductal gray and pontine micturition center. A computer model of this circuit that mimics the switching functions of the bladder and urethra at the onset of micturition is described. Micturition occurs involuntarily in infants and young children until the age of 3 to 5 years, after which it is regulated voluntarily. Diseases or injuries of the nervous system in adults can cause the re-emergence of involuntary micturition, leading to urinary incontinence. Neuroplasticity underlying these developmental and pathological changes in voiding function is discussed.

Innervation of bladder and bowel

The autonomic neuromuscular junction is described and neurotransmission, co-transmission and neuromodulation are defined, as well as the 'chemical coding' of sympathetic, parasympathetic, sensory-motor and intrinsic neurons in the wall of the bladder and bowel. A detailed description of the patterns of innervation of smooth muscle of the bowel, bladder and urethra and of the urethral and anal sphincters by intramural and extrinsic autonomic nerves is presented, and the functional and pharmacological features of this innervation are summarized. Finally, changes in the pattern of innervation and expression of co-transmitters and receptors in the bladder and bowel that occur during development and old age and following trauma, surgery and disease are discussed.

Expression of P2X and P2Y receptors in the intramural parasympathetic ganglia of the cat urinary bladder

The distribution and function of P2X and P2Y receptor subtypes were investigated on intact or cultured intramural ganglia of the cat urinary bladder by immunocytochemistry and calcium-imaging techniques, respectively. Neurons were labeled by all seven P2X receptor subtype antibodies and antibodies for P2Y2, P2Y4, P2Y6, and P2Y12 receptor subtypes with a staining intensity of immunoreactivity in the following order: P2X3=P2Y2=P2Y4=P2Y6=P2Y12>P2X1=P2X2=P2X4>P2X5=P2X6=P2X7. P2Y1 receptor antibodies labeled glial cells, but not neurons. P2X3 and P2Y4 polyclonal antibodies labeled ∼95 and 40% of neurons, respectively. Double staining showed that 100, 48.8, and 97.4% of P2X3 receptor-positive neurons coexpressed choline acetyl transferase (ChAT), nitric oxide synthase (NOS), and neurofilament 200 (NF200), respectively, whereas 100, 59.2, and 97.6% of P2Y4 receptor-positive neurons coexpressed ChAT, NOS, and NF200, respectively. Application of ATP, α,β-methylene ATP, and uridine triphosphate elevated intracellular Ca2+ concentration in a subpopulation of dissociated cultured cat intramural ganglia neurons, demonstrating the presence of functional P2Y4 and P2X3 receptors. This study indicates that P2X and P2Y receptor subtypes are expressed by cholinergic parasympathetic neurons innervating the urinary bladder. The neurons were also stained for NF200, usually regarded as a marker for large sensory neurons. These novel histochemical properties of cholinergic neurons in the cat bladder suggest that the parasympathetic pathways to the cat bladder may be modulated by complex purinergic synaptic mechanisms.

Modulation of insulin-like growth factor-I system of the bladder using a somatostatin analogue in chronic spinalized rats

PURPOSE

We have previously reported the possible role of the insulin-like growth factor-I (IGF-I) system of mitogens in the development of detrusor smooth muscle hyperplasia and hypertrophy after spinal cord injury. We evaluated the in vivo effects of the anti-growth factor somatostatin analogue octreotide on the IGF-I system as well as subsequent changes in bladder smooth muscle hypertrophy and function after spinal cord injury in rats.

MATERIALS AND METHODS

Included in this study were 90 adult female Sprague-Dawley rats weighing 200 to 250 gm. Of the rats 18 served as sham operated controls, while the remaining 72 underwent were spinal cord transection at the level of the T10 vertebra. The spinalized animals were randomly divided into 4 equal groups of 18, of which 1 group served as paraplegic controls. The other 3 groups received octreotide (60 microgram. daily for 4 weeks) delivered via a subcutaneously implanted osmotic pump immediately, 2 and 4 weeks after spinal cord injury. At the end of the experiment (6 to 8 weeks) each group of animals was subdivided into 2 subgroups of 9. In the first group filling cystometrography was done, while in the second subgroup wet bladder weight was estimated and Northern blot analysis was performed.

RESULTS

Mean wet bladder weight plus or minus standard deviation in sham operated and paraplegic controls was 0.11 +/- 0.01 and 0.64 +/- 0.33 gm., respectively (p <0.05). The increase in bladder weight in paraplegic controls was associated with over expression of the IGF-I gene and with marked suppression of IGF binding proteins-3 and 5 compared with sham operated controls. On the other hand, mean wet bladder weight in the animals that received octreotide immediately after spinal cord injury was 0.17 +/- 0.02 gm., which was associated with a dramatic decrease in IGF-I gene expression and increased expression of IGF binding proteins-3 and 5. Mean cystometric bladder capacity in paraplegic controls was 0.48 +/- 0.18 ml. with an associated voiding pressure of 71 +/- 13 cm. water. All paraplegic controls showed detrusor hyperreflexia. In animals that received octreotide immediately after spinal cord injury mean cystometric bladder capacity was 2.49 +/- 1.75 ml. with an associated voiding pressure of 32 +/- 7 cm. water. Detrusor hyperreflexia disappeared in 88.89% of the rats in this group. There were less marked changes in bladder weight (mean 0.24 and 0.29 +/- 0.3 gm.), IGF-I gene expression and its binding proteins and urodynamic parameters when the drug was given 2 and 4 weeks, respectively, after spinal cord injury.

CONCLUSIONS

Modulating the IGF-I system of mitogens in detrusor smooth muscle with consequently decreased bladder hypertrophy and improved urodynamic behavior in spinal cord injured animals using somatostatin analogue could be a possible therapeutic modality in patients with spinal cord injury.

Distribution of NADPH-diaphorase and nitric oxide synthase-containing neurons in the intramural ganglia of guinea pig urinary bladder

The cell population and distribution of NADPH-diaphorase positive and NOS immunoreactive intramural ganglion cells were examined on stretched whole-mount preparations of the guinea pig urinary bladder which was divided into 3 regions: base, body and dome. The results showed that the highest frequency both of NADPH-d and NOS positive neurons was observed in the bladder base. Cell counts in the whole bladder showed that the number of NADPH-d positive neurons was much more than that of NOS immunoreactive neurons. Using neuron specific enolase (NSE) positive neurons as a reference (100%), NADPH-d positive neurons accounted for 84% while NOS immunoreactive neurons only made up 45% of the total neuronal population. These results, along with previous studies on the function of nitric oxide, suggest that nitric oxide may be involved in the relaxation activity in the bladder base during micturition. The significant difference in the number of NADPH-d positive and NOS immunoreactive neurons suggests that the localisation of one enzyme does not necessarily reflect the presence of the other.

Neuropeptides and neurotransmitter-synthesizing enzymes in intrinsic neurons of the human urinary bladder

The expression of neuropeptides, and the enzymes nitric oxide synthase and tyrosine hydroxylase were examined in intramural ganglia of human urinary bladder using single label immunocytochemistry. Scattered ganglia composed of between 1-36 neurons (median 4) were observed in all layers of the lateral wall of the bladder. These contained immunoreactivity to vasoactive intestinal peptide, nitric oxide synthase, neuropeptide Y, and galanin. Neurons within the bladder were heterogeneous with regard to their content of these antigens, with the proportion of immunopositive cells ranging from 58-84%. Occasional neurons with immunoreactivity to the catecholamine-synthesizing enzyme, tyrosine hydroxylase, were also observed. No cell somata, however, were immunoreactive for enkephalin, substance P, calcitonin gene-related peptide or somatostatin. Varicose terminals entering the ganglia were seen to form pericellular baskets surrounding some of the principal ganglion cells. The most prominent pericellular varicosities were those containing calcitonin gene-related peptide- or vasoactive intestinal peptide-immunoreactivity, followed by those with immunoreactivity for enkephalin, neuropeptide Y, or galanin. Less common were pericellular varicosities with substance P-immunoreactivity, which may represent collateral processes of unmyelinated primary sensory fibres, and presumptive noradrenergic processes containing tyrosine hydroxylase. Some calcitonin gene-related peptide-immunoreactive varicosities constituted a distinct type, terminating as large pericellular boutons 2-4 microns in diameter. Fibres containing nitric oxide synthase- or somatostatin-immunoreactivity were not associated with the intramural neurons. The results demonstrate that intrinsic neurons within the human urinary bladder express a number of neuroactive chemicals, and could in principle form circuits with the potential to support integrative activity.

Effects of denervation on muscarinic receptors in the rat bladder

OBJECTIVE

To demonstrate the specific distribution of muscarinic receptors in the rat urinary bladder and to investigate the effects of afferent and efferent denervation on the density and distribution of muscarinic receptors.

MATERIALS AND METHODS

Urinary bladders were obtained from female rats which had been injected with vehicle (control), or neonatally with capsaicin (NC, afferent denervation) or which had their pelvic plexus removed (post-ganglionic denervation, PGD, efferent denervation). Tissue sections were used in radioligand-binding studies and for autoradiography with the muscarinic receptor ligand l-quinuclidinyl[phenyl-4-3H]benzilate (QNB).

RESULTS

Binding of QNB was saturable and specific to a single population of binding sites, with a mean dissociation constant (Kd) of 1.05 +/- 0.14 nM in controls and 0.90 +/- 0.13 nM in rats with PGD. Post-ganglionic denervation caused a 37% increase in maximal binding (Bmax) of QNB from 437.1 +/- 39.1 fmol/mg protein (control group) to 599.1 +/- 4.5 fmol/mg protein (P < 0.02). Autoradiograms revealed muscarinic binding sites over the smooth muscle, but none over the epithelium. Smooth muscle binding sites were doubled after PGD but were unchanged after NC treatment.

CONCLUSION

Muscarinic receptors were localized over the smooth muscle of the rat bladder and were increased after post-ganglionic denervation. This increase may be responsible for the increased sensitivity to muscarinic agonists reported to occur after bladder denervation.

Somatostatin modulates vascular sympathetic neurotransmission in the rabbit ear artery

Somatostatin-like immunoreactivity was localised immunohistochemically in perivascular nerves in the rabbit central ear artery. Whilst somatostatin had no direct action on this vessel, it significantly inhibited noradrenaline-induced, but not alpha, beta-methylene ATP-induced, vasoconstriction. Somatostatin also inhibited contractions elicited by electrical field stimulation showing greater effect at low (16 Hz) compared with high (64 Hz) frequencies, and inhibited the release of tritiated noradrenaline in a concentration-dependent manner. These results confirm that somatostatin is a neuroregulatory peptide, and suggest that it is modulating vascular sympathetic cotransmission of the rabbit central ear artery by acting both prejunctionally to inhibit transmitter release, and postjunctionally to reduce the action of noradrenaline.

Patients with lower motor spinal cord lesion: a decrease of vasoactive intestinal polypeptide, calcitonin gene-related peptide and substance P, but not neuropeptide Y and somatostatin-immunoreactive nerves in the detrusor muscle of the bladder

Specimens of the detrusor muscle of the bladder from four patients with lower motor neurone lesion and three patients with carcinoma of the bladder used as "controls", were studied immunohistochemically for vasoactive intestinal polypeptide, neuropeptide Y, calcitonin-gene related peptide, substance P and somatostatin. The greatest density of nerves in the bladder from "control" patients contained neuropeptide Y, followed in a decreasing order by vasoactive intestinal polypeptide, calcitonin gene-related peptide, substance P and somatostatin. Neuropeptide Y- and vasoactive intestinal polypeptide-immunoreactive nerves were found throughout the smooth muscle and the base of the mucosa, while calcitonin gene-related peptide-, substance P- and somatostatin-immunoreactive nerves were found predominantly in nerve bundles with a few single fibres at the base of the mucosa. Vasoactive intestinal polypeptide-, neuropeptide Y- and calcitonin gene-related peptide-immunoreactive nerves were also located around blood vessels. In patients with lower motor neurone lesion, there was a decrease in the density of vasoactive intestinal polypeptide-, calcitonin gene-related peptide- and substance P-immunoreactive nerves, but there was little change in neuropeptide Y- or somatostatin-immunoreactive nerves. Urinary retention, bladder areflexia and deficient sensation may be directly linked to neuropeptide neuropathy in patients with lower motor neurone lesion.

Colocalization of peptides and a catecholamine-synthesizing enzyme in intramural neurones of the newborn guinea-pig urinary bladder in culture

The patterns of colocalization of somatostatin (SOM), neuropeptide Y (NPY) and the catecholamine-synthesizing enzyme, dopamine beta-hydroxylase (DBH), were examined in intramural neurones in dissociated cell culture preparations from the detrusor muscle of the urinary bladder of the newborn guinea-pig using an elution-restaining immunocytochemical technique. Large numbers of the intramural neurones contained NPY-like (70-85% of the total neuronal population) and SOM-like (60-75%) immunoreactivities, in contrast to a small population (1-6%) of neurones containing immunoreactivity to DBH. Some neurones were immunoreactive to NPY (15-20%) and SOM (5-10%) alone, while 55-70% of the total neuronal population showed immunoreactivity to both NPY and SOM. NPY-like immunoreactive neuronal cell bodies that did not contain SOM were predominantly binucleate, whereas neuronal cell bodies immunoreactive to SOM alone were mainly mononucleate. Although not seen in every culture preparation, neuronal cell bodies containing both NPY-like and DBH-like immunoreactivities were also observed (less than 5% of the total neuronal population), and most, if not all, of these neuronal cell bodies were binucleate. SOM-like and DBH-like immunoreactivities were not seen in the same neuronal cell body throughout this study. These results show that intramural bladder neurones can be divided into distinct subpopulations based upon the coexistence of specific peptides and enzymes, and the possibility that they sustain local integrative and modulatory roles in bladder function is discussed.