Coexistence of nitric oxide synthase, tyrosine hydroxylase and vasoactive intestinal polypeptide in human penile tissue--a triple histochemical and immunohistochemical study

Aging-related NADPH diaphorase positive neurodegenerations in the sacral spinal cord of aged non-human primates

Nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) was used to detect neurodegenerations in aged monkeys. Our previous studies have shown that aging-related NADPH-d positive bodies (ANBs) and megaloneurites appeared in the lumbosacral spinal cord of aged rats and dogs, respectively. To determine the occurrence of megaloneurites and ANBs in non-human primates, we used NADPH-d histochemistry to perform an advanced study of aging-related alterations in aged male monkeys. We identified two distinct abnormal NADPH-d positive alterations, which were expressed as ANBs and megaloneurites, mainly distributed in the superficial dorsal horn, dorsal gray commissure, lateral collateral pathway (LCP) and sacral parasympathetic nucleus of the sacral spinal cord in aged monkeys. Meanwhile, large diameter punctate NADPH-d abnormalities occurred and scattered in the lateral white matter of the LCP and dorsal root entry zone at the same level of megaloneurites in the gray matter. Immunohistochemical results showed that megaloneurites and ANBs are two distinct abnormal alterations, with megaloneurites co-localizing with vasoactive intestinal peptide immunoreactivity, whereas ANBs were not co-localized. Both ANBs and megaloneurites provide consistent evidence that the anomalous NADPH-d alterations in the aged sacral spinal cord are referred to as a specialized aging marker in the pelvic visceral organs in non-human primates.

De novo aging-related NADPH diaphorase positive megaloneurites in the sacral spinal cord of aged dogs

We investigated aging-related changes in nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) in the spinal cord of aged dogs. At all levels of the spinal cord examined, NADPH-d activities were observed in neurons and fibers in the superficial dorsal horn (DH), dorsal gray commissure (DGC) and around the central canal (CC). A significant number of NADPH-d positive macro-diameter fibers, termed megaloneurites, were discovered in the sacral spinal cord (S1-S3) segments of aged dogs. The distribution of megaloneurites was characterized from the dorsal root entry zone (DREZ) into the superficial dorsal horn, along the lateral collateral pathway (LCP) to the region of sacral parasympathetic nucleus (SPN), DGC and around the CC, but not in the cervical, thoracic and lumbar segments. Double staining of NADPH-d histochemistry and immunofluorescence showed that NADPH-d positive megaloneurites co-localized with vasoactive intestinal peptide (VIP) immunoreactivity. We believed that megaloneurites may in part represent visceral afferent projections to the SPN and/or DGC. The NADPH-d megaloneurites in the aged sacral spinal cord indicated some anomalous changes in the neurites, which might account for a disturbance in the aging pathway of the autonomic and sensory nerve in the pelvic visceral organs.

Site-dependent differences in the composite fibers of male pelvic plexus branches: an immunohistochemical analysis of donated elderly cadavers

Background

Although the pelvic autonomic plexus branches are considered to be a mixture of sympathetic and parasympathetic nerves, little is known regarding the composite fibers of the pelvic plexus branches. This study aimed to investigate the immunohistochemical features of sympathetic and parasympathetic nerves in the pelvic autonomic plexus branches.

Methods

Using 10 donated elderly male cadavers, the detailed topohistology of nerve fibers at and around the bladder, seminal vesicle, prostate, and rectum was examined. Neuronal nitric oxide synthase (nNOS) and vasoactive intestinal polypeptide (VIP) were used as parasympathetic nerve markers; tyrosine hydroxylase (TH) was used as a sympathetic nerve marker. The myenteric plexus of the colon was utilized as a positive control.

Results

Most nerve fibers in the bladder, seminal vesicle, prostate, and rectum were both nNOS- and TH-positive. Thus, pelvic plexus branches were classified into two types: 1) triple-positive mixed nerves (nNOS+, VIP+, TH+, thick myelinated fibers + or -) and 2) double-positive mixed nerves (nNOS+, VIP-, TH+, thick myelinated fibers + or -). Notably, triple-positive nerves were localized within the posterosuperior part of the plexus (near the rectum) and travelled anteroinferiorly toward the posterolateral corner of the prostate. The posteriorly and inferiorly located nerves were predominantly composed of parasympathetic, rather than sympathetic, fibers. In contrast, nerve fibers within and along the bladder and seminal vesicle contained either no or few VIP-positive nerves. These superiorly located nerves were characterized by clear sympathetic nerve dominance.

Conclusions

The nerves of the pelvic plexus branches were clearly classified into nerves around the bladder and seminal vesicle (VIP-negative) and nerves around the prostate (VIP-positive). Although nNOS- and VIP-positive nerve fibers are candidate cavernous nerves, cavernous nerve identity cannot be definitively concluded for these nerves in the periprostatic region.

Sympathetic Hyperactivity, Increased Tyrosine Hydroxylase and Exaggerated Corpus Cavernosum Relaxations Associated with Oxidative Stress Plays a Major Role in the Penis Dysfunction in Townes Sickle Cell Mouse

Background

Sickle cell disease patients display priapism that may progress to erectile dysfunction. However, little is known about the pathophysiological alterations of corpus cavernosum in sickle cell disease.

Objective

Thus, this study aimed to evaluate the functional and molecular alterations of sympathetic machinery and nitric oxide—cyclic guanosine monophosphate signaling pathway in Townes transgenic sickle cell disease mice.

Methods

Concentration–response curves to contractile (phenylephrine) and relaxant agents (acetylcholine and sodium nitroprusside) were obtained in corpus cavernosum strips from sickle and C57BL/6 (control) mice. Neurogenic contractions and nitrergic relaxations were obtained using electrical-field stimulation. Measurements of endothelial nitric oxide synthase (eNOS), neuronal nitric oxide synthase (nNOS), phosphodiesterase-5 (PDE5) and α_1A-, α_1B- and α_1D-adrenoceptor mRNA expressions and reactive-oxygen species were performed. Tyrosine hydroxylase phosphorylated at Ser-31 and total tyrosine hydroxylase protein expressions in cavernosal tissues were also measured.

Results

The neurogenic contractions were higher in the sickle cell disease group, in association with elevated tyrosine hydroxylase phosphorylated at Ser-31 and total tyrosine hydroxylase protein expression, as well as increased tyrosine hydroxylase mRNA expression. Likewise, phenylephrine-induced contractions were greater in the sickle mice, whereas α_1A-, α_1B- and α_1D-adrenoceptor mRNA expression remained unchanged. Cavernosal relaxations to acetylcholine, sodium nitroprusside and EFS were higher in sickle mice, accompanied by decreased eNOS and nNOS, along with lower PDE5 mRNA expression. An increase of about 40% in reactive-oxygen species generation in corpus cavernosum from sickle mice was also detected.

Conclusion

Our study shows that decreased nitric oxide bioavailability in erectile tissue due to increased oxidative stress leads to both sympathetic hyperactivity and dysregulation of nitric oxide signaling in corpus cavernosum from Townes sickle mice.

Direct effect of carbon monoxide on relaxation induced by electrical field stimulation in rat corpus cavernosum

Purpose

Carbon monoxide (CO) may mediate smooth muscle relaxation in the rat corpus cavernosum smooth muscle (CCSM). We hypothesized that CO plays a role in neurally derived, frequency-dependent relaxation of rat CCSM.

Materials and Methods

To study the effect of CO on CCSM relaxation induced by electrical field stimulation (EFS), a CCSM bundle was mounted on a force transducer and perfused with Hanks' balanced salt solution at 37℃ with 95% O₂ and 5% CO₂. After 1 hour equilibration with -500 mg of passive tension, contraction of the CCSM bundle was elicited by 10^-5 M phenylephrine, which was continuously added with different concentrations of CO (1%, 2%, and 5%). Frequency-dependent relaxation was induced by EFS trains (0.2 ms at 0.5-32 Hz, for 10 s) repeated at 2 min intervals over 15 min in the presence of adrenergic and muscarinic receptor blocking agents (guanethidine and atropine, respectively). To study the distribution of heme oxygenase-2 (HO-2) in the rat CCSM, we performed immunohistochemical evaluation.

Results

CO produced a dose-dependent enhancement of EFS-induced relaxation. Pretreatment with N^G-nitro-L-arginine (a nitric oxide synthase blocker) greatly reduced the EFS-induced relaxation in the presence of CO (-45%). Pretreatment with zinc protoporphyrin-IX (ZnPP-9, a heme oxygenase inhibitor) had no significant effect on EFS-induced relaxation in the absence or the presence of CO. We found immunoreactivity for HO-2 in CCSM and immunoreactivity for protein gene product 9.5 (PGP 9.5) in nerve fibers.

Conclusions

We conclude that CO produced a dose-dependent enhancement of EFS-induced relaxation in rat CCSM bundles, but neurally derived, frequency-dependent relaxation in the rat CCSM depended mostly on nitric oxide in response to nonadrenergic noncholinergic neurotransmission. Immunoreactivity for HO-2 was found in rat CCSM but not nerve fibers.

Age-related NADPH-diaphorase positive bodies in the lumbosacral spinal cord of aged rats

In the course of a morphological investigation of age-related changes in the rat spinal cord, using nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) histochemistry, we found abundant NADPH-d positive bodies, which were characteristically expressed in the aged lumbosacral spinal cord. Together with a normally stained fiber network and a few neurons, the dense, spheroidal NADPH-d positive bodies occurred in portions of the sacral dorsal spinal cords, such as the dorsal commissural nucleus, intermediolateral nuclei, and superficial dorsal horn, and were scattered throughout the dorsal white column. These NADPH-d positive bodies were occasionally observed in a fibrous structure. Two morphologically distinctive subsets of NADPH-d positive bodies were noted in the spinal cord of rats aged 8 to 36 months: 1) highly-dense spheroidal shapes with sharp edges; 2) moderately-dense spheroidal or multiangular shapes with a central "core" and a peripheral "halo". The quantitative analysis, particularly the stereological measurement, confirmed a gradual increase in the incidence and size of NADPH-d positive bodies with increasing age. With nNOS immunohistochemistry, no corresponding structures to NADPH-d positive bodies were detected in aged rats; thus NADPH-d activity is not always specific to the NO-containing neural structures. The major distribution of the NADPH-d positive bodies in the aged lumbosacral spinal cord indicates some anomalous changes in the neurite, which might account for a disturbance in the aging pathway of the autonomic and sensory nerve in the pelvic visceral organs.

Alpha(1A)-adrenoceptors mediate contractions to phenylephrine in rabbit penile arteries

BACKGROUND AND PURPOSE

Maintained penile erection depends on the absence of alpha-adrenoceptor (alpha-AR) activation and so can be facilitated by alpha-blockers. This study seeks the alpha(1)-AR subtypes involved in order to inform the pro-erectile consequences of subtype selective blockade.

EXPERIMENTAL APPROACH

Wire myography was used with dorsal (nutritional supply) and cavernous (erectile inflow) penile arteries; standard alpha-AR-selective agonists and antagonists were employed to classify responses.

KEY RESULTS

In both penile arteries noradrenaline (NA) and phenylephrine (PE, alpha(1)-AR agonist) caused concentration-dependent contractions. Sensitivity to NA was increased by NA uptake blockers, cocaine (3 microM) and corticosterone (30 microM). PE responses were antagonised by phentolamine (non-selective alpha-AR: dorsal pK(B) 8.00, cavernous 8.33), prazosin (non-subtype-selective alpha(1)-AR: dorsal 8.60, cavernous 8.41) and RS100329 (alpha(1A)-AR selective: dorsal 9.03, cavernous 8.80) but not by BMY7378 (alpha(1D)-AR selective: no effect at 1-100 nM) or Rec15/2615 (alpha(1B)-AR selective: no effect at 1-100 nM). Schild analysis was straightforward in cavernous artery, indicating that PE activates only alpha(1A)-AR. In dorsal artery Schild slopes were low, though alpha(1A)-AR was still indicated. Analysis using UK 14,304 and rauwolscine indicated an alpha(2)-AR component in dorsal artery that may account for low slopes to alpha(1)-AR antagonists.

CONCLUSIONS AND IMPLICATIONS

Penile arteries have a predominant, functional alpha(1A)-AR population with little evidence of other alpha(1)-AR subtypes. Dorsal arteries (nutritional supply) also have alpha(2)-ARs. Thus, alpha-AR blockers with affinity for alpha(1A)-AR or alpha(2)-AR would potentially have pro-erectile properties; the combination of these perhaps being most effective. This should inform the design of drugs to assist/avoid penile erection.

Nitric oxide: a co-modulator of efferent peptidergic neurosecretory cells including a unique octopaminergic neurone innervating locust heart

Our findings suggest that nitric oxide (NO) acts as peripheral neuromodulator in locusts, in which it is commonly co-localized with RF-like peptide in neurosecretory cells. We also present the first evidence for NO as a cardio-regulator in insects. Putative NO-producing neurones were detected in locust pre-genital free abdominal ganglia by NADPH-diaphorase histochemistry and with an antibody against NO synthase (NOS). With both methods, we identified the same 14 somata in each examined ganglion: two dorsal posterior midline somata; six ventral posterior midline somata; and three pairs of lateral somata. A combination of NOS-detection methods with nerve tracing and transmitter immunocytochemistry revealed that at least 12 of these cells were efferent, of which four were identified as peptidergic neurosecretory cells with an antiserum detecting RFamide-like peptides. One of the latter was unequivocally identified as an octopaminergic dorsal unpaired median (DUM) neurone, which specifically projected to the heart ("DUM-heart"). Its peripheral projections revealed by axon tracing appeared as a meshwork of varicose endings encapsulating the heart. NOS-like immunoreactive profiles were found in the heart nerve. NO donors caused a dose-dependent increase in heart rate. This cardio-excitatory effect was negatively correlated to resting heart rate and seemed to be dependent on the physiological state of the animal. Hence, NO released from neurones such as the rhythmically active DUM-heart might exert continuous control over the heart. Possible mechanisms for the actions of NO on the heart and interactions with other neuromodulators co-localized in the DUM-heart neurone (octopamine, taurine, RF-amide-like peptide) are discussed.

Interindividual Variation in Distribution of Extramural Ganglion Cells in the Male Pelvis: A Semi-Quantitative and Immunohistochemical Study Concerning Nerve-Sparing Pelvic Surgery

OBJECTIVE

We examined distribution and numbers of extramural ganglion cells in the male pelvis, classifying them as sympathetic or parasympathetic.

METHODS

Specimens were obtained from 14 formalin-fixed donated male cadavers. Semiserial sections were processed for histologic examination, and for immunohistochemistry using anti-tyrosine hydroxylase (TH) or anti-peptide histidine isoleucine (PHI).

RESULTS

Like those along the sacral sympathetic trunk, most other pelvic ganglion cells were located in and along nerve components. Yet the ganglion cell clusters attached to pelvic viscera accounted for 22% to 38% of ganglion cells. These were seen at the dorsal aspect of the bladder, the bladder/prostate junction, the dorsal aspect of the seminal vesicle, and along the prostate, but not along the extrapelvic pudendal nerve, cavernous tissues including the penile hilum, the rhabdosphincter, retropubic fat or recto-urethral muscle. Two fold interindividual variation was seen for total ganglion cell number (3044 to 6522) in the pelvis. TH-positive and PHI-positive cells intermingled at various ratio in every ganglion cell cluster. Sympathetic TH-positive proportions tended to be site-specific.

CONCLUSIONS

Pelvic autonomic cells exist not only in nerve components but also along viscera. Even nerve-sparing radical prostatectomy can compromise visceral ganglia. Simple classification of pelvic nerve components as sympathetic or parasympathetic would seem misleading given coexistence of both cell types in a ganglion.

Y+ and y+ L arginine transporters in neuronal cells expressing tyrosine hydroxylase

Arginine is a semi-essential amino acid that serves as sole substrate for enzymes involved in diverse cell processes including redox balance via nitric oxide synthase (NOS) and cell proliferation via arginase. Neurons that express nNOS require intracellular arginine to generate nitric oxide (NO). Using a TH+ neuronal cell line (CAD cells), we show that neuronal NO production is largely dependent on extracellular arginine. Although a small intracellular pool exists in CAD cells, the lack of mRNA for argininosuccinate synthase (AS), a rate limiting enzyme for arginine recycling, suggests that intracellular pools are not re-supplied by this mechanism in this sub-class of neurons. Rather, arginine is taken up from the extracellular media by two primary transport systems, the y+ and the y+ L systems. The expression of CAT1, CAT3, y+ LAT1 and y+ LAT2 mRNAs supports the presence of each system. CAD cell arginine transport is depressed by increased extracellular K+ levels and demonstrates that variations in membrane potential control neuronal arginine uptake. Short term exposure to the oxidizing agents, rotenone and Angeli's salt, but not FeSO4, increases arginine transport. The regulation of arginine uptake by physiological factors suggests that arginine supply adapts in a moment-to-moment fashion to the changing needs of the neuron.

The pharmacology of nitric oxide in the peripheral nervous system of blood vessels

Unanticipated, novel hypothesis on nitric oxide (NO) radical, an inorganic, labile, gaseous molecule, as a neurotransmitter first appeared in late 1989 and into the early 1990s, and solid evidences supporting this idea have been accumulated during the last decade of the 20th century. The discovery of nitrergic innervation of vascular smooth muscle has led to a new understanding of the neurogenic control of vascular function. Physiological roles of the nitrergic nerve in vascular smooth muscle include the dominant vasodilator control of cerebral and ocular arteries, the reciprocal regulation with the adrenergic vasoconstrictor nerve in other arteries and veins, and in the initiation and maintenance of penile erection in association with smooth muscle relaxation of the corpus cavernosum. The discovery of autonomic efferent nerves in which NO plays key roles as a neurotransmitter in blood vessels, the physiological roles of this nerve in the control of smooth muscle tone of the artery, vein, and corpus cavernosum, and pharmacological and pathological implications of neurogenic NO have been reviewed. This nerve is a postganglionic parasympathetic nerve. Mechanical responses to stimulation of the nerve, mainly mediated by NO, clearly differ from those to cholinergic nerve stimulation. The naming "nitrergic or nitroxidergic" is therefore proposed to avoid confusion of the term "cholinergic nerve", from which acetylcholine is released as a major neurotransmitter. By establishing functional roles of nitrergic, cholinergic, adrenergic, and other autonomic efferent nerves in the regulation of vascular tone and the interactions of these nerves in vivo, especially in humans, progress in the understanding of cardiovascular dysfunctions and the development of pharmacotherapeutic strategies would be expected in the future.

The role of nitric oxide in penile erection

The functional state of the penis, flaccid or erect is governed by smooth muscle tone. Sympathetic contractile factors maintain flaccidity whilst parasympathetic factors induce smooth muscle relaxation and erection. It is generally accepted that nitric oxide (NO) is the principal agent responsible for relaxation of penile smooth muscle. NO is derived from two principal sources: directly from non-adrenergic non-cholinergic parasympathetic nerves and indirectly from the endothelium lining cavernosal sinusoids and blood vessels in response to cholinergic stimulation. The generation of NO from L-arginine is catalysed by nitric oxide synthase (NOS). There has been controversy over the relative prevalence of endothelial or neuronal NOS within the penis of different animal species. This review examines the role of NO in the penis in detail. Established and new treatments for erectile dysfunction whose effects are mediated via manipulation of the NO pathway are also described.

Cholinergic nerves in human corpus cavernosum and spongiosum contain nitric oxide synthase and heme oxygenase

PURPOSE

To characterize the distribution of cholinergic nerves in the human corpus cavernosum (CC) and spongiosum (CS) using antibodies to the vesicular acetylcholine transporter (VAChT), and to compare this distribution to those of other transmitters/mediators or transmitter/mediator generating enzymes (heme oxygenases: HO-1 and HO-2; neuronal and endothelial NO synthases: nNOS and eNOS; vasoactive intestinal polypeptide: VIP; and tyrosine hydroxylase: TH), and to investigate NO- and carbon monoxide (CO)-mediated effects.

MATERIALS AND METHODS

Immunocytochemistry, confocal laser scanning microscopy, radioimmunoassay, and functional in vitro studies.

RESULTS

Along strands of smooth muscle in the CC and CS, rich numbers of VAChT-, nNOS-, VIP-, TH-, and very few HO-1-immunoreactive (-IR) nerve fibers were observed. Immunoreactivities for VAChT and nNOS, VAChT and VIP, and nNOS and VIP, were generally found in the same varicose nerve terminals. TH-IR nerve fibers or terminals did not contain immunoreactivities for VAChT, NOS or VIP. In the endothelium lining penile arteries, immunoreactivities for eNOS, HO-1, and HO-2 were detected. Single endothelial cells, lining the sinusoidal walls of the CC and CS, were found also to contain eNOS and HO-immunoreactivities. Noradrenaline (NA)-contracted preparations of CC and CS were relaxed by NO, CO, carbachol and by electrical stimulation of nerves. Inhibition of NO synthesis abolished electrically- and carbachol-induced relaxation. In NA-activated strips, relaxation induced by exogenously applied NO, but not those by CO, were accompanied by increases in intracellular levels of cyclic GMP.

CONCLUSIONS

VAChT, NOS and VIP are found in the same nerve terminals within the human CC and CS, suggesting that these terminals comprise a distinct population of parasympathetic, cholinergic nerves. Endothelially derived NO and the HO/CO system may have a complementary role in penile erection.

Cholinergic nerves in human corpus cavernosum and spongiosum contain nitric oxide synthase and heme oxygenase

PURPOSE

To characterize the distribution of cholinergic nerves in the human corpus cavernosum (CC) and spongiosum (CS) using antibodies to the vesicular acetylcholine transporter (VAChT), and to compare this distribution to those of other transmitters/mediators or transmitter/mediator generating enzymes (heme oxygenases: HO-1 and HO-2; neuronal and endothelial NO synthases: nNOS and eNOS; vasoactive intestinal polypeptide: VIP; and tyrosine hydroxylase: TH), and to investigate NO- and carbon monoxide (CO)-mediated effects.

MATERIALS AND METHODS

Immunocytochemistry, confocal laser scanning microscopy, radioimmunoassay, and functional in vitro studies.

RESULTS

Along strands of smooth muscle in the CC and CS, rich numbers of VAChT-, nNOS-, VIP-, TH-, and very few HO-1-immunoreactive (-IR) nerve fibers were observed. Immunoreactivities for VAChT and nNOS, VAChT and VIP, and nNOS and VIP, were generally found in the same varicose nerve terminals. TH-IR nerve fibers or terminals did not contain immunoreactivities for VAChT, NOS or VIP. In the endothelium lining penile arteries, immunoreactivities for eNOS, HO-1, and HO-2 were detected. Single endothelial cells, lining the sinusoidal walls of the CC and CS, were found also to contain eNOS and HO-immunoreactivities. Noradrenaline (NA)-contracted preparations of CC and CS were relaxed by NO, CO, carbachol and by electrical stimulation of nerves. Inhibition of NO synthesis abolished electrically- and carbachol-induced relaxation. In NA-activated strips, relaxation induced by exogenously applied NO, but not those by CO, were accompanied by increases in intracellular levels of cyclic GMP.

CONCLUSIONS

VAChT, NOS and VIP are found in the same nerve terminals within the human CC and CS, suggesting that these terminals comprise a distinct population of parasympathetic, cholinergic nerves. Endothelially derived NO and the HO/CO system may have a complementary role in penile erection.

No colocalization of immunoreactivities for VIP and neuronal NOS, and a differential relation to cGMP-immunoreactivity in bovine penile smooth muscle

The distribution of immunoreactivity (IR) for the neuropeptide vasoactive intestinal polypeptide (VIP) and neuronal nitric oxide synthase (nNOS) in the bovine retractor penis muscle (RP) and penile artery (PA) was studied by using two different methods. The distribution of these immunoreactivities was also compared with that of the immunoreactivity for cyclic guanosine monophosphate (cGMP). In both tissues the nerve fibers and terminals immunoreactive for VIP had a distribution that was completely different from that of the nerve fibers and terminals immunoreactive for nNOS. This contrasts with the previous observations in penile smooth muscle of other species. In the RP, as well as in the PA, many of the VIP-IR fibers were also immunoreactive for neurofilaments (NF), whereas the nNOS-IR fibers were consistently devoid of NF-IR. Stimulation with sodium nitroprusside, a nitric oxide donor, considerably increased cGMP-IR in the smooth muscle cells in both RP and PA, and in several nerve fibers in PA. Many of these cGMP-IR nerve fibers exhibited nNOS-IR, whereas none of them was immunoreactive for VIP. Our results suggest that the degree of coexistence of VIP-IR and nNOS-IR in the nerve fibers and terminals innervating penile smooth muscle show wide species differences. They also suggest that the mechanisms by which VIP could be involved in neurogenic penile erection may vary between species.

NO synthase in cholinergic nerves and NO-induced relaxation in the rat isolated corpus cavernosum

1. In the rat corpus cavernosum (CC), the distribution of immunoreactivity for neuronal and endothelial NO synthase (nNOS and eNOS), and the pattern of NOS-immunoreactive (-IR) nerves in relation to some other nerve populations, were investigated. Cholinergic nerves were specifically immunolabelled with antibodies to the vesicular acetylcholine transporter protein (VAChT). 2. In the smooth muscle septa surrounding the cavernous spaces, and around the central and helicine arteries, the numbers of PGP- and tyrosine hydroxylase (TH)-IR terminals were large, whereas neuropeptide Y (NPY)-, VAChT-, nNOS-, and vasoactive intestinal polypeptide (VIP)-IR terminals were found in few to moderate numbers. 3. Double immunolabelling revealed that VAChT- and nNOS-IR terminals, VAChT- and VIP-IR terminals, nNOS-IR and VIP-IR terminals, and TH- and NPY-IR terminals showed coinciding profiles, and co-existence was verified by confocal laser scanning microscopy. TH immunoreactivity was not found in VAChT-, nNOS-, or VIP-IR nerve fibres or terminals. 4. An isolated strip preparation of the rat CC was developed, and characterized. In this preparation, cumulative addition of NO to noradrenaline (NA)-contracted strips, produced concentration-dependent, rapid, and almost complete relaxations. Electrical field stimulation of endothelin-1-contracted preparations produced frequency-dependent responses: a contractile twitch followed by a fast relaxant response. After cessation of stimulation, there was a slow relaxant phase. Inhibition of NO synthesis, or blockade of guanylate cyclase, abolished the first relaxant phase, whereas the second relaxation was unaffected. 5. The results suggest that in the rat CC, nNOS, VAChT- and VIP-immunoreactivities can be found in the same parasympathetic cholinergic neurons. Inhibitory neurotransmission involves activation of the NO-system, and the release of other, as yet unknown, transmitters.

Innervation of the fibro-elastic type of the penis: an immunohistochemical study in the male pig

The occurrence and colocalization of several biologically active neuropeptides, catecholamine-, acetylcholine- or nitric oxide-synthesizing enzymes-tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (D beta H), choline acetyl-transferase (ChAT) and nitric oxide synthase (NOS I), respectively, as well as the vesicular acetylcholine transporter (VAChT) were investigated in the penile glans (GP), corpus and crura (CP), as well as in the retractor penis muscle (RPM) of juvenile and adult boars. Immunohistochemistry revealed that nerves immunoreactive (IR) to TH, D beta H, vasoactive intestinal polypeptide (VIP) and somatostatin (SOM) were the most numerous, followed (in decreasing order of density) by nerves IR to NOS, neuropeptide Y (NPY), substance P (SP), calcitonin gene-related peptide (CGRP), galanin (GAL), Leu5-enkephalin (LENK) and ChAT/VAChT. The CP contained the largest number of nerve fibres followed by the RPM, GP and corpus. Enzyme/peptide-containing nerves were associated with both the vascular and non-vascular penile structures. However, differences existed for their density and intrapenile distribution. Nerve terminals IR for different combinations of VIP, GAL or SOM were more frequent than those IR for NOS or CGRP in the non-vascular penile structures while the vasculature and the RPM received a prominent TH/D beta H-, VIP-, SOM- or NOS-IR nerve input. The present data indicate that the porcine penis receives nerve fibres that exhibit diverse chemical codes and that differences in the chemical coding of the nerve fibres may depend on their penile target-structure.

Distribution of nitric oxide synthase implies a regulation of circulation, smooth muscle tone, and secretory function in the human prostate by nitric oxide

BACKGROUND

Nitric oxide (NO) is suggested as a mediator involved in the regulation of smooth muscle tone, blood flow, and secretory function of the genitourinary tract and originates from different NO synthase (NOS) isoforms located in endothelial, neuronal, and epithelial structures. The aim of the present study was to determine the location of endothelial and neuronal NOS in the human prostate.

METHODS

Histochemical NADPH-diaphorase (NADPH-d) staining, ultrastructural NADPH examination, and NOS immunohistochemistry were performed on histologically verified nonmalignant prostate tissue from normal nonobstructive and hyperplastic obstructive human prostates.

RESULTS

In the prostatic tissue, NADPH-d staining and immunohistochemistry with bNOS antibody revealed the existence of a dense nitrinergic innervation of glandular epithelium, fibromuscular stroma, and blood vessels. NADPH-d reaction in glandular epithelium was not confirmed by ecNOS or bNOS immunohistochemistry. In benign prostatic hyperplasia (BPH), the nitrinergic innervation is reduced. The vascular distribution of ecNOS provides evidence for a segmental differentiation of the NO-mediated vascular regulation.

CONCLUSIONS

NO plays an important role in the autonomic innervation of all compartments of prostatic tissue. In obstructive BPH, the nitrinergic innervation is reduced compared to that in normal prostate tissue. Further studies are necessary to elucidate the complex role of NO in the prostate.

Neurotransmission and the contraction and relaxation of penile erectile tissues

The balance between contractant and relaxant factors controls the smooth muscle of the corpus cavernosum and determines the functional state of the penis (detumescence and flaccidity versus tumescence and erection). Noradrenaline contracts both the corpus cavernosum and penile vessels, mainly via stimulation of alpha(1)-adrenoceptors. Recent investigations have demonstrated the presence of several subtypes of alpha 1-adrenoceptors (alpha(1A), alpha(1B), and alpha(1D)) in the human corpus cavernosum and also that the noradrenaline-induced contraction in this tissue is probably mediated by two or, possibly, three receptor subtypes. Even if much of the available in vitro information suggests that endothelins (ETs) may be of importance for mechanisms of detumescence and flaccidity, the role of the peptides in the control of penile smooth-muscle tone in vivo is unclear, as is the question as to whether they can contribute to erectile dysfunction. For further evaluation of the clinical importance of ETs in penile physiology and pathophysiology, clinical studies on ET-receptor antagonists would be of interest. Neurogenic nitric oxide (NO) has been considered the most important factor for relaxation of penile vessels and the corpus cavernosum, but recent studies in mice lacking neurogenic NO synthase (NOS) have shown these animals to have normal erections. This focuses interest on the role of endothelial NOS and on other agents released from nerves or endothelium. For the time being the most effective means of inducing penile erection in men involves the intracavernous administration of prostaglandin E1 (PGE1). PGE1 may act partly by increasing intracellular concentrations of cyclic adenosine monophosphate (cAMP). Recent results obtained with the adenylate cyclase stimulator forskolin suggest that penile smooth-muscle relaxation leading to penile erection can be achieved through the cAMP pathway. Thus, transmitters and agents acting through this second-messenger system may significantly contribute to relaxation of penile smooth muscle and to erection.