Nerve endings in the human prostate

Generation and Regulation of Spontaneous Contractions in the Prostate

Spontaneous myogenic contractions have been shown to be significantly upregulated in prostate tissue collected from men with Benign Prostatic Hyperplasia (BPH), an extremely common disorder of the ageing male. Although originally thought likely to be involved in 'housekeeping' functions, mixing prostatic secretions to prevent stagnation, these spontaneous myogenic contractions provide a novel opportunity to understand and treat BPH. This treatment potential differs from previous models, which focused exclusively on attenuating nerve-mediated neurogenic contractions. Previous studies in the rodent prostate have provided an insight into the mechanisms underlying the regulation of myogenic contractions. 'Prostatic Interstitial Cells' (PICs) within the prostate appear to generate pacemaker potentials, which arise from the summation of number of spontaneous transient depolarisations triggered by the spontaneous release of Ca²⁺ from internal stores and the opening of Ca²⁺-activated Cl^- channels. Pacemaker potentials then conduct into neighbouring smooth muscle cells to generate spontaneous slow waves. These slow waves trigger the firing of 'spike-like' action potentials, Ca²⁺ entry and contraction, which are not attenuated by blockers of neurotransmission. However, these spontaneous prostatic contractions can be modulated by the autonomic nervous system. Here, we discuss the mechanisms underlying rodent and human prostate myogenic contractions and the actions of existing and novel pharmacotherapies for the treatment of BPH. Understanding the generation of human prostatic smooth muscle tone will confirm the mechanism of action of existing drugs, inform the identification and effectiveness of new pharmacotherapies, as well as predict patient outcomes.

Contractility and pacemaker cells in the prostate gland

PURPOSE

We focused on the current opinion on mechanisms generating stromal tone in the prostate gland.

MATERIALS AND METHODS

We selected the guinea pig as the main species for investigation since its prostate has a high proportion of smooth muscle that undergoes age related changes similar in many respects to that in humans. The main techniques that we used were tension recording and electrophysiology.

RESULTS

We previously reported distinct electrical activity and cell types in the prostate, and speculated on their functional roles. We believe that a specialized group of c-kit immunoreactive prostatic interstitial cells that lie between glandular epithelium and smooth muscle stroma have a role similar to that of gastrointestinal interstitial cells of Cajal, generating the pacemaker signal that manifests as slow wave activity and triggers contraction in smooth muscle cells in guinea pig prostates.

CONCLUSIONS

Since changes in muscle tone are involved in the etiology of age dependent prostate specific conditions such as benign prostatic hyperplasia, knowledge of the electrical properties of the various prostatic cell types and their interactions with each other, with nerves and with the hormonal environment, and how these factors change with age is of considerable medical importance.

The laminin binding integrin alpha6beta1 in prostate cancer perineural invasion

Metastasizing prostate tumor cells invade along nerves innervating the encapsulated human prostate gland in a process known as perineural invasion. The extracellular matrix laminin class of proteins line the neural route and tumor cells escaping from the gland express the laminin binding integrin alpha6beta1 as a prominent cell surface receptor. Integrin alpha6beta1 promotes aggressive disease and supports prostate tumor cell metastasis to bone. Laminins and their integrin receptors are necessary for the development and maintenance of the peripheral nervous system, indicating the potential role for integrin receptors in directing prostate tumor cell invasion on nerves during perineural invasion.

Mechanistic investigation of the adrenergic induction of ventral prostate hyperplasia in mice

BACKGROUND

The norepinephrine (NE) analog phenylephrine has previously been shown to induce atypical prostate hyperplasia in rats. The objective of the present study was to provide further insight into the mechanism of phenylephrine-induced prostate growth.

METHODS

Adult male C57/BL6 mice were given daily subcutaneous injection of phenylephrine, isoproterenol, or phenylephrine in combination with BMY7378, cyclazosin, RS100329, or yohimbine, and the effects on ventral prostate histology, and proliferative and apoptotic indices determined. Phenylephrine was also administered in combination with testosterone in castrated mice.

RESULTS

Atypical prostatic hyperplasia characterized by piling up and/or papillary infolding of epithelial cells with concomitant stromal smooth muscle hyperplasia was seen in adult mice given subcutaneous injection of phenylephrine daily for 26 days. Phenylephrine induced hyperplasia was more severe proximally and was associated with significantly reduced rates of apoptosis (but no change in cell proliferation) in both stromal and epithelial compartments. Only the alpha(1A)-adrenoceptor selective subtype antagonist RS100329 abrogated the phenylephrine-induced hyperplasia. Using selective antibodies, the alpha(1A-1)-adrenoceptor subtype was predominantly localized to the stromal compartments of the mouse and rat ventral prostates. The effects of phenylephrine were mediated independent of testicular androgens.

CONCLUSIONS

Prostatic hyperplasia in mice occurs as a consequence of subchronic administration of the sympathomimetic phenylephrine. Response to phenylephrine is mediated by the alpha(1A)-adrenoceptor, which predominates in the stroma of the rodent ventral prostate. Conceivably, therefore, phenylephrine could directly modulate prostate stromal growth, and indirectly modulate epithelial growth in a paracrine fashion. We cannot, however, rule out the contribution of other indirect effects such as hypoxia/reperfusion or effects on intermediary metabolism.

Immunohistochemical properties and spinal connections of pelvic autonomic neurons that innervate the rat prostate gland

Autonomic innervation of the prostate gland supplies the acini, and non-vascular and vascular smooth muscle. The activity of each of these tissues is enhanced by sympathetic outflow, whereas the role of the parasympathetic nervous system in this organ is unclear. In the present study, a range of methods was applied in rats to determine the location of autonomic neurons supplying this gland, the immunohistochemical properties of these neurons, the spinal connections made with the postganglionic pathways and the distribution of various axon types within the gland. Injection of the retrograde tracer, FluoroGold, into the ventral gland visualised neurons within the major pelvic ganglion and sympathetic chain. Fluorescence immunohistochemical studies on the labelled pelvic neurons showed that most were nonadrenergic (also containing neuropeptide Y, NPY), the others being non-noradrenergic and containing either vasoactive intestinal peptide (VIP) or NPY. Sympathetic dye-labelled neurons were identified by the presence of varicose nerve terminals stained for synaptophysin on their somata following lesion of sacral inputs. Parasympathetic innervation of dye-labelled neurons was identified by continued innervation after hypogastric nerve lesion. Most noradrenergic prostate-projecting neurons were sympathetic, as were many of the non-noradrenergic VIP neurons. Parasympathetic prostate-projecting neurons were largely non-noradrenergic and contained either VIP or NPY. All substances found in retrogradely labelled somata were located in axons within the prostate gland but had slightly different patterns of distribution. The studies have shown that there are a significant number of non-noradrenergic sympathetic prostate-projecting neurons, which contain VIP.

Fine structure of adrenergic nerve fibers in human periodontal ligament

The presence of adrenergic nerve fibers was demonstrated ultrastructurally in the human periodontal ligament obtained from extracted premolar teeth from 8 young patients. The nerve endings were located close to arterioles. The results suggest that they seem to control blood flow in the human periodontal ligament.

Studies on the structure and intrinsic innervation of the normal human prostate

Prostates from eight adult males (age range 17-63 years) were employed in this investigation. Six glands were obtained from multiorgan transplantation donors at the time of organ harvesting, and two additional glands, at routine post-mortem. Microscopic examination has shown that the majority of acini in the peripheral parts of the gland were individually relatively small and lined by an epithelium two to three cells in thickness. In contrast, acini in the central part of the gland were usually large and contained numerous prominent epithelial folds within the lumen. On the basis of morphology, a clear distinction between peripheral and central acini was not observed. The distribution of autonomic ganglia both within and adjacent to the prostate was studied, and nerve cell bodies containing both acetylcholinesterase (AChE) activity and neuropeptide immunoreactivity were identified. The distribution and density of AChE-positive nerves associated with smooth muscle in either the peripheral or central parts of the prostate were indistinguishable. In addition, the majority of acini in peripheral and central regions possessed a rich subepithelial plexus of autonomic nerves. VIP-positive nerve fibers were found in relation to the epithelium lining acini in central and peripheral regions of the gland. In contrast, nerves possessing NPY immunoreactivity occurred only in relation to the smooth muscle trabeculae of the prostate.

Electron microscopic study on the innervation of the human axillary sweat glands

The innervation of human axillary sweat glands was studied at electron microscopic level. Nerve endings with many small agranular vesicles and few large dense-cored vesicles were found outside the basement membrane of the secretory coils. These nerve endings can be classified as cholinergic. This result confirms the previous knowledge that axillary sweat glands are innervated by sympathetic cholinergic nerves.

Nerve endings in human sympathetic ganglia

Forty-eight human sympathetic ganglia from 22 sympathectomies were examined ultrastructurally after one of three different fixations: (1) glutaraldehyde + osmium tetroxide, (2) glutaraldehyde + potassium dichromate + osmium tetroxide, or (3) potassium permanganate. Three different kinds of synapsing nerve ending could be identified after all fixation schedules. Type 1: "Cholinergic," containing small, agranular vesicles 40-60 nm in diameter (75% of all vesicles) and some large granular vesicles (100 nm in diameter). The number of type 1 profiles decreased with increasing age. Type 2: "Adrenergic," containing small granular vesicles 40-70 nm in diameter (over 90% of the vesicles). Type 3: "Nonadrenergic, noncholinergic," characterized by large opaque vesicles 80 -160 nm in diameter (over 50% of all vesicles). The frequencies of the types were counted after potassium permanganate fixation: type 1 - 71%, type 2 - 23%, and type 3 - 6%. In addition, at least two types of nerve profiles were observed which did not form synapses: (1) profiles entirely filled with mitochondria (mitochondrial accumulation), and (2) large nerve profiles full of different kinds of vesicles, myelin figures, and mitochondria (axonal dilatation). It is concluded that the sympathetic ganglion cells receive cholinergic and adrenergic innervation and also a third type of innervation, the possible peptidergic nature of which is discussed.

Immunohistochemical demonstration of VIP, [Met5]-and [Leu5]-enkephalin immunoreactive nerve fibres in the human prostate and seminal vesicles

The distribution of nerves containing immunoreactivity for the VIP and enkephalins has been demonstrated in the human prostate and seminal vesicles using the immunoperoxidase bridge. VIP-containing nerves were detected in both organs studied mainly in association with the epithelium, while nerves containing ELI seemed to be related to smooth muscle. Compared with the distribution of adrenergic and cholinergic nerves in the prostate marked differences in the density of the innervation were detected. The possible nature of these peptide-containing nerves is discussed.