Parasympathetic innervation of cutaneous blood vessels by vasoactive intestinal polypeptide-immunoreactive and acetylcholinesterase-positive nerves: histochemical and experimental study on rat lower lip

Skin neuropathy and immunomodulation in diseases

Skin is a vital barrier tissue of the body. Immune responses in the skin must be precisely controlled, which would otherwise cause severe disease conditions such as psoriasis, atopic dermatitis, or pathogenic infection. Research evidence has increasingly demonstrated the essential roles of neural innervations, i.e., sensory and sympathetic signals, in modulating skin immunity. Notably, neuropathic changes of such neural structures have been observed in skin disease conditions, implicating their direct involvement in various pathological processes. An in-depth understanding of the mechanism underlying skin neuropathy and its immunomodulatory effects could help reveal novel entry points for therapeutic interventions. Here, we summarize the neuroimmune interactions between neuropathic events and skin immunity, highlighting the current knowledge and future perspectives of this emerging research frontier.

The prostate in women: an updated histological and immunohistochemical profile of the female periurethral glands and their relationship to an implanted midurethral sling

BACKGROUND

There is evidence of glandular tissue in the region of the anterior vaginal wall-female periurethral tissue (AVW-FPT) that has similar morphology and immunohistochemistry to the prostate in men. Surgical injury to this tissue has been suggested as a potential cause of sexual dysfunction following midurethral sling (MUS) procedures. However, the anatomy and embryology of these glands have not been fully resolved. This has led to difficulties in classifying this tissue as a prostate and defining its clinical significance related to MUS procedures.

AIM

To describe the histological and immunohistochemical characteristics of the female periurethral glands using markers of prostate tissue and innervation and to examine their anatomical relationships to an implanted MUS.

METHODS

Using gross and fine dissection, the AVW-FPT was dissected from 9 cadavers. Prior to dissection, 2 cadavers underwent simulation of the MUS procedure by a urogynecologist. Samples were paraffin embedded and serially sectioned. Immunohistochemistry was performed using markers of prostate tissue and innervation.

OUTCOMES

Redundant immunohistochemical localization of markers for prostatic tissue and innervation of the glandular tissue of the AVW-FPT, including the region of MUS implantation.

RESULTS

Female periurethral glands were immunoreactive for markers of male prostatic tissue, including prostate-specific antigen, androgen receptor, HOXB13, and NKX3.1. Markers of innervation (protein gene product 9.5, choline acetyl transferase, and vasoactive intestinal polypeptide) also localized to certain regions of the glandular tissue and associated blood supply. Surgical simulation of the MUS procedure demonstrated that some periurethral glands are located in close proximity to an implanted sling.

CLINICAL TRANSLATION

The AVW-FPT contains glandular tissue in the surgical field of MUS implantation. Iatrogenic damage to the female periurethral glands and the associated innervation during surgery could explain the negative impacts on sexual dysfunction reported following MUS procedures.

STRENGTHS AND LIMITATIONS

This is the first study to characterize the female periurethral glands using markers of prostatic tissue in concert with markers of general and autonomic innervation and characterize their anatomical relationships within the surgical field of MUS implantation. The small sample size is a limitation of this study.

CONCLUSION

We provide further evidence that the AVW-FPT contains innervated glands that are phenotypically similar to the male prostate and may share a common embryonic origin. The microscopic and immunohistochemical features of the periurethral glands may be indicative of their functional capacity in sexual responses. The location of these glands in the surgical field of MUS procedures underscores the clinical significance of this tissue.

Differences in the regulatory mechanism of blood flow in the orofacial area mediated by neural and humoral systems

Marked blood flow (BF) changes mediated by the autonomic neural and humoral systems may be important for orofacial hemodynamics and functions. However, it remains questionable whether differences in the autonomic vasomotor responses mediated by neural and humoral systems exist in the orofacial area. This study examined whether there are differences in changes in the BF and vascular conductance (VC) between the masseter muscle and lower lip mediated by autonomic neural and humoral systems in urethane-anesthetized rats. Electrical stimulation of the central cut end of the lingual nerve elicited BF increases in the masseter (mainly cholinergic) and lower lip (mainly non-cholinergic), accompanied by an increase in arterial blood pressure (ABP), while cervical sympathetic trunk stimulation consistently decreased BF at both sites. The lingual nerve stimulation induced a biphasic change in the VC in the masseter, consisting of an initial decrease and a successive increase. This decrease in VC was positively correlated with changes in ABP and diminished by guanethidine. Cervical vagus nerve stimulation also induced BF increases at both sites; the increases were greater in the masseter than in the lower lip. Adrenal nerve stimulation and isoproterenol administration induced BF increases in the masseter but not in the lower lip. These results indicate that cholinergic parasympathetic-mediated hemodynamics evoked by trigeminal somatosensory inputs are closely related to ABP changes. The sympathetic nervous system, including the sympathoadrenal system and visceral inputs, may be more involved in hemodynamics in the muscles than in epithelial tissues in the orofacial area.

Effect of the parasympathetic vasodilation on temperature regulation via trigeminal afferents in the orofacial area

The skin temperature (T_m) of the orofacial area influences orofacial functions and is related to the blood flow (BF). Marked increases in BF mediated by parasympathetic vasodilation may be important for orofacial T_m regulation. Therefore, we examined the relationship between parasympathetic reflex vasodilation and orofacial T_m in anesthetized rats. Electrical stimulation of the central cut end of the lingual nerve (LN) elicited significant increases in BF and T_m in the lower lip. These increases were significantly reduced by hexamethonium, but not atropine. VIP agonist increased both BF and T_m in the lower lip. The activation of the superior cervical sympathetic trunk (CST) decreased BF and T_m in the lower lip; however, these decreases were significantly inhibited by LN stimulation. Our results suggest that parasympathetic vasodilation plays an important role in the maintaining the hemodynamics and T_m in the orofacial area, and that VIP may be involved in this response.

Pre- and postnatal development of the otic ganglion in humans

Only a few papers exist dealing with the development and aging of the autonomic nervous system - and even rarer are studies that investigated the otic ganglion. Using a special trepan, we removed and investigated 172 samples from 86 corpses, ranging from 20 weeks of gestational age (GA) to 95 years of age. The aim of the study was to measure different morphometric parameters of the ganglionic neurons in order to study age-related changes from early development until old age. Fetuses show the highest numerical density of neurons. Then, in the first years of life, a rapid growth of the cytoplasm takes place, which is the main reason for the neuronal growth and the increase of the general size of the otic ganglion at this age. Also, the number of satellite cells increases till puberty. In adults, the parameters are relatively stable over decades and decrease slowly, in contrast to the steep increase in the first years of life. Moreover, neuronal degeneration, storage of pigments, neuro-axonal dystrophy, and lymphocytic infiltrates increase with age.

A pilot study on skin potential recordings as a measure of nociception in pain-free dogs and humans, and in dogs with persistent pain

The Pain Trace™ device can detect changes in the skin's electrical potentials claimed to be associated with pain related alterations in the sympathetic and parasympathetic nervous system activity. Positive voltages represent the absence of major pain, whereas negative voltages represent moderate to severe pain. Unlike in humans and horses, no baseline skin potential recordings have been reported in dogs. In study Part 1 baseline skin potentials were recorded in healthy dogs and compared to readings obtained in human volunteers. In dogs, data were recorded with electrodes placed at three separate sites: neck, axilla, and thorax. In humans, data were collected from the palms. Readings over a 90-second period were averaged and comparisons between groups were performed using the Kruskal-Wallis test. All voltage recordings were positive. Readings in dogs had greater variability. Recordings from the thorax were more homogeneous, this being the reason why this site was chosen for study Part 2. No significant differences in recordings were noted between pain-free dogs and humans. The main hypothesis was that shifting from positive to negative skin potential voltages serves as an indicator of canine patients sensing moderate to severe pain. Therefore, we obtained preoperative readings from dogs with cranial cruciate ligament disease that were experiencing associated persistent pain, and compared these data with readings from pain-free dogs (thorax). In dogs undergoing surgery, all pre-surgery voltage readings were positive and thus no consistent relationship between skin potential recordings and pain perception could be established. Further investigation is needed to confirm any relationship between skin potential and pain severity in dogs.

Parasympathetic reflex vasodilation in the cerebral hemodynamics of rats

We investigated the role of parasympathetic reflex vasodilation in the regulation of the cerebral hemodynamics, and whether GABAA receptors modulate the response. We examined the effects of activation of the parasympathetic fibers through trigeminal afferent inputs on blood flow in the internal carotid artery (ICABF) and the cerebral blood vessels (rCBF) in parietal cortex in urethane-anesthetized rats. Electrical stimulation of the central cut end of the lingual nerve (LN) elicited intensity- and frequency-dependent increases in ICABF that were independent of changes in external carotid artery blood flow. Increases in ICABF were elicited by LN stimulation regardless of the presence or absence of sympathetic innervation. The ICABF increases evoked by LN stimulation were almost abolished by the intravenous administration of hexamethonium (10 mg kg(-1)) and were reduced significantly by atropine administration (0.1 mg kg(-1)). Although the LN stimulation alone had no significant effect on rCBF, LN stimulation in combination with a blocker of the GABAA receptor pentylenetetrazole increased the rCBF markedly. This increase in rCBF was reduced significantly by the administration of hexamethonium and atropine. These observations indicate that the increases in both ICABF and rCBF are evoked by parasympathetic activation via the trigeminal-mediated reflex. The rCBF increase evoked by LN stimulation is thought to be limited by the GABAA receptors in the central nervous system. These results suggest that the parasympathetic reflex vasodilation and its modulation mediated by GABA receptors within synaptic transmission in the brainstem are involved in the regulation of the cerebral hemodynamics during trigeminal afferent inputs.

Rat whisker movement after facial nerve lesion: evidence for autonomic contraction of skeletal muscle

Vibrissal whisking is often employed to track facial nerve regeneration in rats; however, we have observed similar degrees of whisking recovery after facial nerve transection with or without repair. We hypothesized that the source of non-facial nerve-mediated whisker movement after chronic denervation was from autonomic, cholinergic axons traveling within the infraorbital branch of the trigeminal nerve (ION). Rats underwent unilateral facial nerve transection with repair (N=7) or resection without repair (N=11). Post-operative whisking amplitude was measured weekly across 10weeks, and during intraoperative stimulation of the ION and facial nerves at ⩾18weeks. Whisking was also measured after subsequent ION transection (N=6) or pharmacologic blocking of the autonomic ganglia using hexamethonium (N=3), and after snout cooling intended to elicit a vasodilation reflex (N=3). Whisking recovered more quickly and with greater amplitude in rats that underwent facial nerve repair compared to resection (P<0.05), but individual rats overlapped in whisking amplitude across both groups. In the resected rats, non-facial-nerve-mediated whisking was elicited by electrical stimulation of the ION, temporarily diminished following hexamethonium injection, abolished by transection of the ION, and rapidly and significantly (P<0.05) increased by snout cooling. Moreover, fibrillation-related whisker movements decreased in all rats during the initial recovery period (indicative of reinnervation), but re-appeared in the resected rats after undergoing ION transection (indicative of motor denervation). Cholinergic, parasympathetic axons traveling within the ION innervate whisker pad vasculature, and immunohistochemistry for vasoactive intestinal peptide revealed these axons branching extensively over whisker pad muscles and contacting neuromuscular junctions after facial nerve resection. This study provides the first behavioral and anatomical evidence of spontaneous autonomic innervation of skeletal muscle after motor nerve lesion, which not only has implications for interpreting facial nerve reinnervation results, but also calls into question whether autonomic-mediated innervation of striated muscle occurs naturally in other forms of neuropathy.

Perivascular innervation: a multiplicity of roles in vasomotor control and myoendothelial signaling

The control of vascular resistance and tissue perfusion reflect coordinated changes in the diameter of feed arteries and the arteriolar networks they supply. Against a background of myogenic tone and metabolic demand, vasoactive signals originating from perivascular sympathetic and sensory nerves are integrated with endothelium-derived signals to produce vasodilation or vasoconstriction. PVNs release adrenergic, cholinergic, peptidergic, purinergic, and nitrergic neurotransmitters that lead to SMC contraction or relaxation via their actions on SMCs, ECs, or other PVNs. ECs release autacoids that can have opposing actions on SMCs. Respective cell layers are connected directly to each other through GJs at discrete sites via MEJs projecting through holes in the IEL. Whereas studies of intercellular communication in the vascular wall have centered on endothelium-derived signals that govern SMC relaxation, attention has increasingly focused on signaling from SMCs to ECs. Thus, via MEJs, neurotransmission from PVNs can evoke distinct responses from ECs subsequent to acting on SMCs. To integrate this emerging area of investigation in light of vasomotor control, the present review synthesizes current understanding of signaling events that originate within SMCs in response to perivascular neurotransmission in light of EC feedback. Although often ignored in studies of the resistance vasculature, PVNs are integral to blood flow control and can provide a physiological stimulus for myoendothelial communication. Greater understanding of these underlying signaling events and how they may be affected by aging and disease will provide new approaches for selective therapeutic interventions.

Peripheral choline acetyltransferase in rat skin demonstrated by immunohistochemistry

Conventional choline acetyltransferase immunohistochemistry has been used widely for visualizing central cholinergic neurons and fibers but not often for labeling peripheral structures, probably because of their poor staining. The recent identification of the peripheral type of choline acetyltransferase (pChAT) has enabled the clear immunohistochemical detection of many known peripheral cholinergic elements. Here, we report the presence of pChAT-immunoreactive nerve fibers in rat skin. Intensely stained nerve fibers were distributed in association with eccrine sweat glands, blood vessels, hair follicles and portions just beneath the epidermis. These results suggest that pChAT-positive nerves participate in the sympathetic cholinergic innervation of eccrine sweat glands. Moreover, pChAT also appears to play a role in cutaneous sensory nerve endings. These findings are supported by the presence of many pChAT-positive neuronal cells in the sympathetic ganglion and dorsal root ganglion. Thus, pChAT immunohistochemistry should provide a novel and unique tool for studying cholinergic nerves in the skin.

Role of parasympathetic nerves and muscarinic receptors in allergy and asthma

Parasympathetic nerves control the symptoms and inflammation of allergic diseases primarily by signaling through peripheral muscarinic receptors. Parasympathetic signaling targets classic effector tissues such as airway smooth muscle and secretory glands and mediates acute symptoms of allergic disease such as airway narrowing and increased mucus secretion. In addition, parasympathetic signaling modulates inflammatory cells and non-neuronal resident cell types such as fibroblasts and smooth muscle contributing to chronic allergic inflammation and tissue remodeling. Importantly, muscarinic antagonists are experiencing a rebirth for the treatment of asthma and may be useful for treating other allergic diseases.

Occurrence of parasympathetic vasodilator fibers in the lower lip of the guinea-pig

The present study was designed to examine whether there are parasympathetic vasodilator fibers in the lower lip of the guinea-pig. Electrical stimulation of the central cut end of the lingual nerve of guinea-pigs evoked intensity- and frequency-dependent decreases in lower lip blood flow and systemic arterial blood pressure (SABP). Pretreatment with guanethidine, a postganglionic sympathetic nerve blocker and antihypertensive drug (30 mg kg(-1), s.c., 24 h prior to experiments), reduced the magnitude of the decrease in SABP while the intensity- and frequency-dependent increases of the lip blood flow occurred by the lingual nerve stimulation only on the side ipsilateral to stimulation. Increases in the lip blood flow evoked by lingual nerve stimulation in guanethidine pretreated guinea-pigs were reduced by hexamethonium (an autonomic ganglion cholinergic blocker) in a dose-dependent manner. When fluoro-gold (a retrograde neural tracer) was injected into the lower lip, labeled neurons were observed in the ipsilateral otic ganglion. The present study indicates the presence of parasympathetic vasodilator fibers originating from the otic parasympathetic ganglion in the guinea-pig lower lip, similar to those reported previously in rats, cats, rabbits and humans.

Neuronal Control of Skin Function: The Skin as a Neuroimmunoendocrine Organ

This review focuses on the role of the peripheral nervous system in cutaneous biology and disease. During the last few years, a modern concept of an interactive network between cutaneous nerves, the neuroendocrine axis, and the immune system has been established. We learned that neurocutaneous interactions influence a variety of physiological and pathophysiological functions, including cell growth, immunity, inflammation, pruritus, and wound healing. This interaction is mediated by primary afferent as well as autonomic nerves, which release neuromediators and activate specific receptors on many target cells in the skin. A dense network of sensory nerves releases neuropeptides, thereby modulating inflammation, cell growth, and the immune responses in the skin. Neurotrophic factors, in addition to regulating nerve growth, participate in many properties of skin function. The skin expresses a variety of neurohormone receptors coupled to heterotrimeric G proteins that are tightly involved in skin homeostasis and inflammation. This neurohormone-receptor interaction is modulated by endopeptidases, which are able to terminate neuropeptide-induced inflammatory or immune responses. Neuronal proteinase-activated receptors or transient receptor potential ion channels are recently described receptors that may have been important in regulating neurogenic inflammation, pain, and pruritus. Together, a close multidirectional interaction between neuromediators, high-affinity receptors, and regulatory proteases is critically involved to maintain tissue integrity and regulate inflammatory responses in the skin. A deeper understanding of cutaneous neuroimmunoendocrinology may help to develop new strategies for the treatment of several skin diseases.

Trigeminal nerve-mediated reflex arterial blood pressure decrease and vasodilatation in lower lip of the rabbit

We measured the effects of electrical stimulation of the central cut end of the lingual nerve on lower lip blood flow (LBF) and on arterial blood pressure in urethane-anesthetized, artificially ventilated, cervically vagosympathectomized rabbits. Different effects were observed depending on the stimulus frequency. Increasing the stimulus frequency above 5 Hz produced progressively larger ipsilateral LBF increases until the optimal frequency was reached at 20 Hz. In contrast, stimulation at above 0.5 Hz evoked progressively larger decreases in both contralateral LBF and arterial blood pressure until the optimal frequency was reached at around 10 and 2 Hz, respectively. Thus, the optimal stimulus frequencies for the ipsilateral LBF increase and the arterial blood pressure decrease were widely different. The lingual nerve-evoked change (i.e., fall) in arterial blood pressure showed a significant correlation with the contralateral LBF decrease, but not with the ipsilateral LBF increase. Prior administration of hexamethonium at 10 mg/kg markedly reduced both the ipsilateral LBF increase and arterial blood pressure decrease, although it was more effective against the former than against the latter. Pretreatment with scopolamine (muscarinic-receptor antagonist, 0.1 mg/kg), phentolamine (alpha-adrenoceptor antagonist, 0.1 mg/kg), or propranolol (beta-adrenoceptor antagonist, 0.1 mg/kg) failed to affect either response. However, 1.0 mg/kg phentolamine significantly reduced both responses (P<0.05). These results indicate that, in the rabbit, the LN-evoked reflex increase in ipsilateral LBF is (a) largely independent of any concomitant arterial blood pressure change and (b) probably due to active vasodilatation mediated via parasympathetic mechanisms. In contrast, the evoked decrease in contralateral LBF was proportional to the decrease in arterial blood pressure, suggesting that the former was secondary to the latter.

Differences between tooth stimulation and capsaicin-induced neurogenic vasodilatation in human gingiva

Animal experiments have shown that the application of capsaicin to oral mucosa leads to a neurogenic inflammation associated with blood flow elevations in gingivomucosal tissues. In this investigation, we measured the tooth stimulation and capsaicin-evoked blood flow responses in maxillary gingiva in humans to study whether axon-reflex-mediated vasodilatation crosses the midline of the maxilla. The vasoactive reactions were mapped by laser Doppler imaging. Unilateral stimulation of alveolar mucosa and attached gingiva by capsaicin evoked a distinct neurogenic vasodilatation in ipsilateral gingiva, which rapidly attenuated at the midline. Capsaicin stimulation of alveolar mucosa provoked clear inflammatory reactions. In contrast to capsaicin stimuli, tooth stimulation produced symmetrical vasodilatations bilaterally in the gingiva. The ipsilateral responses were significantly smaller during tooth stimulation than during capsaicin stimuli. Analysis of these data suggests that capsaicin-induced inflammatory reactions in gingivomucosal tissues do not cross the midline in the anterior maxilla. The enhanced reaction found during stimulation of alveolar mucosa indicates that alveolar mucosa is more sensitive to chemical irritants than attached gingiva.

Expression of neuropeptides and growth-associated protein 43 (GAP-43) in cutaneous and mucosal nerve structures of the adult rat lower lip after mental nerve section

The reinnervation of the adult rat lower lip has been investigated after unilateral section of the mental nerve. Rats were sacrificed at 4, 7, 9, 14, 30, and 90 days after the operation. A further group of animals with section of the mental nerve and block of the alveolar nerve regeneration, was sacrificed at 14 days. Specimens were processed for immunocytochemistry with antibodies against PGP 9.5, GAP-43 or neuropeptides (CGRP, SP and VIP). Four days after nerve section, axonal degeneration seems evident in the mental nerve branches and inside skin and mucosa. GAP-43 immunoreactivity is intense in the mental nerve 7 days after nerve section and it reaches its maximal expression and distribution in peripheral nerve fibres at 14 days. At 30 days, the decline in its expression is associated with the increase of PGP9.5-, SP-, and CGRP immunopositivity. VIP is observed only in perivascular fibres at all times observed. Present results suggest that, after sensory denervation of the rat lip, nerve fibres in skin and mucosa remain at lower density than normal. The different time courses in the expression of neuropeptides and GAP-43 suggest a possible early involvement of GAP-43 in peripheral nerve regeneration.

Parasympathetic nerve fibers invade the upper dermis following sensory denervation of the rat lower lip skin

The sympathetic division of the autonomic nervous system is known to play a role in the genesis of neuropathic pain. In the skin of the rat lower lip (hairy skin), sympathetic and parasympathetic fibers normally innervate the same blood vessels in the lower dermis but do not occur in the upper dermis. However, we have shown that sympathetic fiber migration into the upper dermis occurs following mental nerve lesions (Ruocco et al. [2000] J. Comp. Neurol. 422:287-296). As sensory denervation has a dramatic effect on sympathetic fiber innervation patterns in the rat lower lip skin, we decided to investigate the possible changes in the other autonomic fiber type in the skin-the parasympathetic fiber. Sensory denervation of the rat lower lip was achieved by bilateral transection of the mental nerve, and animals were allowed to recover for 1-8 weeks. Lower lip tissue was processed for double-labeling light microscopic immunocytochemistry (ICC), using antibodies against substance P (SP), which labels a subpopulation of peptidergic sensory fibers, and against the vesicular acetycholine transporter (VAChT), as a marker for parasympathetic fibers. In sham-operated rats, SP-immunoreactive (IR) sensory fibers were found in the epidermis and upper and lower dermal regions, whereas VAChT-IR fibers were confined to the lower dermis. Mental nerve lesions induced the gradual disappearance of SP-IR fibers from all skin layers accompanied by the progressive migration of VAChT-IR fibers into the upper dermis. Cholinergic fiber migration was evident by the second week post surgery, and the ectopic innervation of the upper dermis by these fibers persisted even at the last time point studied (8 weeks) when SP-IR fibers have completely regrown. VAChT-IR fibers were observed in the upper dermis, well above the opening of the sebaceous glands into the hair follicles. These results show that considerable changes occur in the innervation patterns of parasympathetic fibers following mental nerve lesions.

Skin blood vessels are simultaneously innervated by sensory, sympathetic, and parasympathetic fibers

Despite the known major role of skin blood vessel innervation in blood flow control, particularly in disease, little information on the co-innervation of blood vessels by sensory and autonomic fibers and the relationships of these fibers to one another is available. To fill this gap, we performed a light and electron microscopic analysis of the innervation of skin vessels by sensory and autonomic fibers by using the rat and monkey lower lips as a model. In rats, double-labeling immunocytochemistry revealed that combinations of fibers immunoreactive for substance P (SP) and dopamine-beta-hydroxylase (DbetaH), SP and vesicular acetylcholine transporter (VAChT), as well as DbetaH and VAChT occurred only around blood vessels in the lower dermis. All fiber types travelled in parallel and in close proximity to one another. In the upper dermis, blood vessels were innervated by SP-containing fibers only. Although nerve terminals displayed synaptic vesicles, synaptic specializations were never observed, suggesting that, in this territory, these fibers do not establish synaptic contacts. Quantification of the distance between the various immunoreactive terminals and their presumptive targets (smooth muscle cells and endothelial cells) revealed that both sympathetic and parasympathetic fibers were significantly closer to the endothelial cell layer and smooth muscle cells compared with sensory fibers. In monkeys, double-labeling immunocytochemistry was performed for SP-DbetaH and SP-VAChT only. The results obtained are similar to those found in rats; however, the fiber density was greater in monkeys. Our findings suggest that the regulation of skin microcirculation might be the result of the coordinated functions of sensory and autonomic fibers.

Pathophysiology of pruritus in atopic dermatitis: an overview

Pruritus is an essential feature of atopic dermatitis (AD) and the diagnosis of active AD cannot be made without the history of itching. Because of the high impact on life quality, most of the patients measure the severity of eczema by the intensity of pruritus rather than appearance of skin lesions. However, although pruritus is a cardinal symptom of AD, its mechanism and association with the cutaneous nervous system is not completely understood. Recently, a considerable progress has been achieved in clarifying the complex pathophysiology of pruritus in AD. As a cutaneous sensory perception, itch requires excitation of neuropeptide-containing free nerve endings of unmyelinated nociceptor fibers. It is well known that histamine and acetylcholine provoke itch by direct binding to 'itch receptors' and several mediators such as neuropeptides, proteases or cytokines indirectly via histamine release. Interestingly, some variations of these complex mechanisms could be demonstrated in patients with AD. This review highlights the recent knowledge of different mechanisms which may be involved in regulating pruritus in patients with AD potentially leading to new therapeutic applications for the treatment of itch in AD.

Blood flow increase in the human lip after high-intensity tooth stimulation is not based on cholinergic mechanisms

The purpose of this study was to investigate whether parasympathetic cholinergic pathways are involved in the regulation of orofacial blood flow. The effect of atropin (1 mg, iv.) on blood flow responses in the lower lip, nose and hand during painful tooth stimulation was studied in healthy human subjects (n=8). In all subjects, tooth stimulation caused a long lasting vasodilatation in the lower lip. During stimulation there was a transient elevation in heart rate (HR) and blood pressure (BP) concomitantly with a blood flow decrease in the finger and nose. With atropin, the pain-induced HR and BP elevations and blood flow reductions in the nose and finger were decreased. However, the pain-induced blood flow increase in the lip was not changed. This study indicates that the tooth stimulation-induced vasodilatation in the lip is not based on parasympathetic cholinergic mechanisms.

The importance of stimulus site and intensity in differences of pain-induced vascular reflexes in human orofacial regions

Studies in anaesthetized animals have indicated that noxious stimulation may produce marked blood flow changes in various orofacial structures, but the influence of painful stimulation on the blood flow regulation of the orofacial area of humans has been studied only to a limited extent. The purpose of this investigation was to study whether there are differences in temporal and spatial patterns of pain-induced vasoactive reflexes between various orofacial regions and hand in healthy human volunteers. Dynamic changes in blood flow in various orofacial regions elicited by painful stimulation of the tooth and finger were measured by means of Laser Doppler imaging (LDI) and computer-assisted infrared thermography (IRT). Blood flow of the finger was recorded by laser Doppler flowmetry (LDF) and plethysmography (PLET). During both stimulus paradigms there was a transient elevation in heart rate (HR) and blood pressure (BP). At the same time there was a significant blood flow decrease in the finger (LDF, PLET) and in the nose (LDI, IRT). In contrast to tooth stimulation, finger stimulation caused a more marked blood flow reduction in the finger. Only high intensity tooth stimulation, but not finger stimulation, caused a long-lasting vasodilatation both in lower and upper lip. The blood flow changes in the lips were not correlated with changes in systemic blood pressure or heart rate. In the cheek, there were no marked flow changes during either finger or tooth stimulation. These data indicate that painful tooth (regional) stimulation, but not finger (remote) stimulation, can induce a long-lasting vasodilatation in parts of orofacial tissues which cannot be explained by changes in central cardiovascular parameters. This tooth-stimulation-induced blood flow increase supports the hypothesis of a special vasodilator reflex mechanism in the orofacial area. Furthermore, tooth-stimulation-induced vasoconstriction in the nose and dilatation in the lips indicate that separate vasoactive reflex mechanisms may exist for different orofacial regions.

PGH(2)-TxA(2)-receptor blockade restores vasoreactivity in a new rodent model of genetic hypertension

The purpose of this study was to determine whether activation of prostaglandin H(2)-thromboxane A(2) (PGH(2)-TxA(2)) receptors impedes vasodilation in the in situ peripheral microcirculation of spontaneously hypertensive hamsters, a new rodent model of high-renin genetic hypertension. Using intravital microscopy, we found that vasodilation elicited by suffusion of acetylcholine and vasoactive intestinal peptide (VIP), two neurotransmitters localized in perivascular nerves in the peripheral circulation, on the in situ cheek pouch was significantly attenuated in spontaneously hypertensive hamsters relative to age- and genetically matched normotensive hamsters (P < 0.05). However, nitroglycerin-induced vasodilation was similar in both groups. Pretreatment with SQ-29548, a selective and potent PGH(2)-TxA(2)-receptor antagonist, restored acetylcholine- and VIP-induced vasodilation in spontaneously hypertensive hamsters. SQ-29548 had no significant effects on resting arteriolar diameter and on nitroglycerin-induced vasodilation in both groups. SQ-29548 slightly but significantly potentiated VIP- but not acetylcholine-induced vasodilation in normotensive hamsters. Collectively, these data indicate that activation of PGH(2)-TxA(2) receptors impedes agonist-induced vasodilation in the in situ cheek pouch of spontaneously hypertensive hamsters. We suggest that this model is suitable for studying the role of prostanoids in mediating vasomotor dysfunction observed in genetic hypertension.

Morphological and cytochemical characteristics of periodontal Ruffini ending under normal and regeneration processes

Current knowledge on the Ruffini endings, primary mechanoreceptors in the periodontal ligament is reviewed with special reference to their cytochemical features and regeneration process. Morphologically, they are characterized by extensive ramifications of expanded axonal terminals and an association with specialized Schwann cells, called lamellar or terminal Schwann cells, which are categorized, based on their histochemical properties, as non-myelin-forming Schwann cells. Following nerve injury, the periodontal Ruffini endings of the rat incisor ligament can regenerate more rapidly than Ruffini endings in other tissues. During regeneration, terminal Schwann cells associated with the periodontal Ruffini endings migrate into regions where they are never found under normal conditions. Also during regeneration, alterations in the expression level of various bioactive substances occur in both axonal and Schwann cell elements in the periodontal Ruffini endings. Neuropeptide Y, which is not detected in intact periodontal Ruffini endings, is transiently expressed in their regenerating axons. Growth-associated protein-43 (GAP-43) is expressed transiently in both axonal and Schwann cell elements during regeneration, while this protein is localized in the Schwann sheath of periodontal Ruffini endings under normal conditions. The expression of calbindin D28k and calretinin, both belonging to the buffering type of calcium-binding proteins, was delayed in periodontal Ruffini endings, compared to their morphological regeneration. As the importance of axon-Schwann cell interactions has been proposed, further investigations are needed to elucidate their molecular mechanism particularly the contribution of growth factors during the regeneration as well as development of the periodontal Ruffini endings.

Nervous control of blood flow in the orofacial region

The blood vessels of orofacial tissues are innervated by cranial parasympathetic, superior cervical sympathetic, and trigeminal nerves, a situation somewhat different from that seen in body skin. This review summarizes our current knowledge of the nervous control of blood flow in the orofacial region, and focuses on what we know of the respective roles of sympathetic, parasympathetic, and trigeminal sensory nerves in the regulation of blood flow in this region, with particular attention being paid to the mutual interaction between them.

Neuropeptide immunoreactivity in ligature-induced neuromas of the inferior alveolar nerve in the ferret

Injury to branches of the trigeminal nerve can sometimes result in persistent dysaesthesia. In an attempt to understand the aetiology of this condition we are currently investigating changes which occur at the injury site. In the present study we have examined the expression of seven neuropeptides, all of which have been implicated in nociceptive transmission, or have previously been shown to have altered expression following nerve injury. In 20 adult ferrets the inferior alveolar nerve was sectioned and ligated, and recovery permitted for 3 days, 8 days, 3 weeks, 6 weeks or 12 weeks. Longitudinal sections of the neuromas were processed using immunohistochemical techniques to quantify the expression of substance P, calcitonin gene-related peptide, vasoactive intestinal polypeptide, galanin, somatostatin, enkephalin and neuropeptide Y. After 3 days, all of the neuropeptides were expressed at the injury site. In the neuromas examined after longer recovery periods these levels of expression had declined and were similar to those found in the contralateral controls. This initial high level, followed by a decline, parallels the incidence of ectopic neural activity recorded electrophysiologically in the same model. It is, therefore, possible that the accumulation of neuropeptides at the injury site may play a role in the initiation or modulation of ectopic neural activity.

Ca(2+)-activated K+ channels in rat otic ganglion cells: role of Ca2+ entry via Ca2+ channels and nicotinic receptors

1. Intracellular recordings were made from neurones in the rat otic ganglion in vitro in order to investigate their morphological, physiological and synaptic properties. We took advantage of the simple structure of these cells to test for a possible role of calcium influx via nicotinic acetylcholine receptors during synaptic transmission. 2. Cells filled with biocytin comprised a homogeneous population with ovoid somata and sparse dendritic trees. Neurones had resting membrane potentials of -53 +/- 0.7 mV (n = 69), input resistances of 112 +/- 7 M omega, and membrane time constants of 14 +/- 0.9 ms (n = 60). Upon depolarization, all cells fired overshooting action potentials which were followed by an apamin-sensitive after-hyperpolarization (AHP). In response to a prolonged current injection, all neurones fired tonically. 3. The repolarization phase of action potentials had a calcium component which was mediated by N-type calcium channels. Application of omega-conotoxin abolished both the repolarizing hump and the after-hyperpolarization suggesting that calcium influx via N-type channels activates SK-type calcium-activated potassium channels which underlie the AHP. 4. The majority (70%) of neurones received innervation from a single preganglionic fibre which generated a suprathreshold excitatory postsynaptic potential mediated by nicotinic acetylcholine receptors. The other 30% of neurones also had one or more subthreshold nicotinic inputs. 5. Calcium influx via synaptic nicotinic receptors contributed to the AHP current, indicating that this calcium has access to the calcium-activated potassium channels and therefore plays a role in regulating cell excitability.

Origin of nerves supplying the posterior portion of lumbar intervertebral discs in rats

STUDY DESIGN

The authors studied the origin of nerves supplying the posterior portion of lumbar intervertebral discs in rats by resection of the sympathetic trunks.

OBJECTIVE

To understand discogenic low back pain from the innervation of the lumbar intervertebral discs.

SUMMARY OF BACKGROUND DATA

The afferent pathways of discogenic low back pain have not been studied thoroughly. It has been reported that stimulation of an inflamed lower spinal nerve root elicits leg pain but not low back pain and that stimulation of the posterior portion of lumbar intervertebral discs evokes only low back pain. These facts suggest that pain sensation from the posterior portion of lumbar discs is not transmitted via the lower spinal nerve roots.

METHODS

Forty-five Wistar rats were used. Seven days after the resection of sympathetic trunks with ganglia at different levels, the whole lumbar spine was stained by an acetylcholinesterase histochemical method. The posterior portions of lumbar intervertebral discs were observed.

RESULTS

The dense nerve network on the posterior portion of lumbar intervertebral discs had disappeared almost completely after total resection of bilateral sympathetic trunks at L2-L6. However, there was a slight decrease in the network after bilateral single-level resection or unilateral multisegmental resection.

CONCLUSIONS

The results showed that the posterior portion of lumbar intervertebral discs was innervated by the sympathetic nerves multisegmentally and bilaterally.

Neural control of pulpal blood flow

Blood flow of mammalian dental pulp is under both remote and local control. There is evidence for the existence of parasympathetic nerves in the pulp, but functionally the cholinergic influence is weak, and the physiological significance of this autonomic system seems to be low. The evidence for sympathetic vasoconstrictor nerves in the pulp is robust, and there is convincing support for the contention that these nerves play a physiological role, operating via release of noradrenaline and neuropeptide Y. However, there is no significant functional evidence in support of sympathetic beta-adrenoceptor-mediated vasodilation in the pulp. The local control of blood flow involves a subset of intradental sensory nerves. By virtue of their neuropeptide content, these afferent fibers cause vasodilation and inhibit sympathetic vasoconstriction in response to painful stimulation of the tooth. Such locally governed control may serve to meet immediate demands of the pulp tissue. A locally triggered reflex activation of sympathetic nerves in the pulp may modulate this control and limit its magnitude. Thus, there are competitive interactions between local and remote vascular controls which may be put out of balance in the injured and inflamed dental pulp.

Reflex parasympathetic vasodilatation in facial skin

1. The present report summarizes data from recent studies dealing with parasympathetic innervation of blood vessels in the lower lips (gingiva) of cats. 2. A study using the HRP tracing technique shows that blood vessels in the lower lip are innervated by postganglionic fibres originating in the otic ganglion, but not in the pterygopalatine ganglion. 3. There is a dual innervation of the cat lower lip by two groups of parasympathetic vasodilator fibres; in one case, fibres originating from the facial nerve root are distributed to the lower lip via chorda tympani nerve and in the other, fibres emanating from the glossopharyngeal nerve root project to the lower lip via the otic ganglion. 4. Parasympathetic reflex vasodilatation can be elicited by activation of the trigeminal (somatic), vagus (visceral), chorda tympani (gustatory) and nasal (chemical and mechanical) stimulation in the lower lips of cat. 5. Parasympathetic reflex vasodilatation elicited by somatic stimulation is mediated via the otic ganglion but not via the pterygopalatine ganglion, indicating that parasympathetic neurons, particularly those running as efferents in the glossopharyngeal nerve, are involved in the vasodilatation elicited by somatic, visceral and nasal stimulation.

Pentylenetetrazole-induced parasympathetic blood flow increase in the lower lip of the cat

The pentylenetetrazole (30 mg/kg i.v.)-induced blood flow increase in cat lip was more marked on the sympathectomized side than on the intact side (P < 0.01). This difference is probably dependent on the degree of simultaneous activation of the sympathetic nerve elicited by pentylenetetrazole administration. The blood flow increases were markedly suppressed by prior treatment with hexamethonium (10 mg/kg i.v.), an autonomic ganglion blocker (P < 0.01). Combined section of the facial and glossopharyngeal nerve roots completely abolished the blood flow increases elicited by pentylenetetrazole administration (P < 0.01), but section of either the facial or glossopharyngeal nerve root alone failed to produce complete abolition (P < 0.05). These results indicate that the relevant parasympathetic vasodilator fibers originate not only from the glossopharyngeal, but also the facial nerves and that both participate in pentylenetetrazole-induced vasodilatation in the cat lower lip.

Teeth and tooth nerves

(1) Although our knowledge on teeth and tooth nerves has increased substantially during the past 25 years, several important issues remain to be fully elucidated. As a result of the work now going on at many laboratories over the world, we can expect exciting new findings and major break-throughs in these and other areas in a near future. (2) Dentin-like and enamel-like hard tissues evolved as components of the exoskeletal bony armor of early vertebrates, 500 million years ago, long before the first appearance of teeth. It is possible that teeth developed from tubercles (odontodes) in the bony armor. The presence of a canal system in the bony plates, of tubular dentin, of external pores in the enamel layer and of a link to the lateral line system promoted hypotheses that the bony plates and tooth precursors may have had a sensory function. The evolution of an efficient brain, of a head with paired sense organs and of toothed jaws concurred with a shift from a sessile filter-feeding life to active prey hunting. (3) The wide spectrum of feeding behaviors exhibited by modern vertebrates is reflected by a variety of dentition types. While the teeth are continuously renewed in toothed non-mammalian vertebrates, tooth turnover is highly restricted in mammals. As a rule, one set of primary teeth is replaced by one set of permanent teeth. Since teeth are richly innervated, the turnover necessitates a local neural plasticity. Another factor calling for a local plasticity is the relatively frequent occurrence of age-related and pathological dental changes. (4) Tooth development is initiated through interactions between the oral epithelium and underlying neural crest-derived mesenchymal cells. The interactions are mediated by cell surface molecules, extracellular matrix molecules and soluble molecules. The possibility that the initiating events might involve a neural component has been much discussed. With respect to mammals, the experimental evidence available does not support this hypothesis. In the teleost Tilapia mariae, on the other hand, tooth germ formation is interrupted, and tooth turnover ceases after local denervation. (5) Prospective dental nerves enter the jaws well before onset of tooth development. When a dental lamina has formed, a plexus of nerve branches is seen in the subepithelial mesenchyme. Shortly thereafter, specific branches to individual tooth primordia can be distinguished. In bud stage tooth germs, axon terminals surround the condensed mesenchyme and in cap stage primordia axons grow into the dental follicle.(ABSTRACT TRUNCATED AT 400 WORDS)

A study of cholinergic and beta-adrenergic components in the regulation of blood flow in the tooth pulp and gingiva in man

In 10 subjects, laser Doppler flowmetry was used to study whether cholinergic or beta-adrenergic pathways are involved in the control of tooth pulp blood flow (PBF) in response to isometric hand grip and the cold pressor test. We also examined if differences exist between the regulation of blood flow in the tooth pulp and the nearby gingiva (GBF). Isometric hand grip (35% of maximum force, 2 min) and the subsequent ischaemia (2 min) induced a brief rise in PBF and a more long-lasting rise in GBF. Atropine increased heart rate about by 40% and changed the pulpal response to a fall in flow, without altering gingival flow. Propranolol, causing a 20% reduction in heart rate, had no effect on either flow during the actual test, but induced a rise in GBF after the ischaemic period. The cold pressor test (2 min at 0.5 degrees C) resulted in a reduction in PBF and GBF, unaffected by the blocking drugs. With atropine, however, PBF increased immediately after this test. The relative changes in arterial pressure and heart rate were unaffected by the drugs. Our study has demonstrated the existence of cholinergic nervous vasodilation in vessels serving the tooth pulp. Non-adrenergic non-cholinergic mechanisms probably contribute to the evoked rise in GBF during exercise. Beta-adrenoceptors are involved in the control of GBF immediately after isometric exercise. While the two tests under control conditions evoked mostly parallel changes in PBF and GBF, the use of blocking agents showed that blood flow is controlled by different mechanisms in the two adjacent vascular beds.

Innervation of the cat lip by two groups of parasympathetic vasodilator fibres

1. Electrical stimulation of the peripheral cut ends of the chorda tympani nerve proper (CTNP) and the chorda-lingual nerve (CLN) elicited a blood flow increase in the ipsilateral lower lip, tongue and submandibular gland in a stimulus intensity-dependent manner in anaesthetized cats. 2. Pretreatment with hexamethonium (1.0 mg kg-1, i.v.), an autonomic ganglionic blocker, significantly reduced the CTNP-induced blood flow increases in all of the above three sites as well as the CLN-induced blood flow in the lower lip, but it had no effects on the CLN-induced blood flow increases in the tongue and submandibular gland. 3. The CTNP stimulation-induced lower lip blood flow was not influenced by sectioning the lingual nerve proper, but it was abolished by section of either the CLN or the inferior alveolar nerve (IAN) in the mandibular canal. 4. The lip blood flow increases elicited reflexly by electrical stimulation of the upper gingiva, the central cut ends of the mylohyoid nerve and CLN were not affected by cutting of the CTNP, but were markedly reduced by pretreatment with hexamethonium and abolished by the section of the inferior alveolar nerve just distal to the mylohyoid nerve. These observations imply that the parasympathetic vasodilator fibres involved in trigeminally induced reflex vasodilatation responses do not travel with the CTNP. 5. These results suggest that there is a dual innervation of the cat lower lip by two groups of parasympathetic vasodilator fibres; in one case fibres originating from the facial nerve root are distributed to the lower lip via the CTNP, CLN and IAN and in the other fibres emanating from the glossopharyngeal nerve root project to the lower lip via the mandibular nerve and the IAN.

Reflex vasodilatation in the cat lip evoked by stimulation of vagal afferents

In 36 cats under nembutal anaesthesia, stimulation of the central end of the cut vagus nerve caused blood flow to increase in only the ipsilateral side in six cats (17%) and in the bilateral sides in 30 cats (83%) in the lower lips. Pretreatment with hexamethonium to block nicotinic synapses in autonomic ganglia resulted in a time-dependent reduction of the reflex vasodilator response, while phentolamine, propranolol (alpha-, beta-adrenoreceptor antagonists) and tripelennamine (histamine receptor antagonist) had no effect. Pretreatment with atropine (muscarinic receptor antagonist) showed a slight, but not statistically insignificant attenuation of the reflex vasodilatation. Ipsilateral section of either the glossopharyngeal nerve root or the inferior alveolar nerve completely abolished the reflex vasodilator response elicited by central vagal stimulation. The reflex vasodilator response induced by stimulation of the central end of the cut vagus nerve was abolished by topical capsaicin application on the central cut ends of the vagus nerve but not by capsaicin on the inferior alveolar nerve. These results suggest that there is a cutaneous reflex vasodilator system that can be activated via capsaicin-sensitive afferent fibres in the vagus nerve. Parasympathetic vasodilator fibres of this system emerge from the brain stem with the glossopharyngeal nerve and reach the blood vessels in the cat mandibular lip via the inferior alveolar nerve.

Somatosensory afferents in the parasympathetic vasodilator reflex in cat lip

Somato-parasympathetic reflexive vasodilatation elicited by activation of the nociceptors in the oro-facial areas of the cat was investigated. Changes in lower lip blood flow monitored by a laser Doppler flowmeter took place in pentobarbital-anesthetized and artificially respirated cats. Pinch and heat stimulation of the oro-facial areas evoked a blood flow increase similar to that of electrically induced vasodilatation. Sustained increased responses in blood flow were obtained when a 1% capsaicin solution was applied to the tongue. These results show that the C-polymodal nociceptor is a strong candidate for a receptor that provokes somato-parasympathetic vasodilatation. Capsaicin-insensitive nerve fibers, however, also participate because electrical stimulation of the capsaicin-treated tongue evoked vasodilatation. The correlation between noxious stimulation-induced vasodilatation and systemic blood pressure change also is discussed.

Selective excitation of parasympathetic nerve fibers to elicit the vasodilatation in cat lip

Electrical stimulation of the tongue and the proximal cut end of the lingual nerve caused a blood flow to increase in a stimulus-intensity dependent manner in the ipsilateral lower lip of the cats. Pretreatment with hexamethonium (an autonomic ganglionic blocker, 1.0 mg/kg) abolished the vasodilator response, while atropine, phentolamine, propranolol and tripelennamine had no effect on these vasoresponses. Ipsilateral sections of either the glossopharyngeal nerve root, inferior alveolar nerve or mental nerve at the main mental foramen, but not at the posterior mental foramen, abolished the vasodilator response caused by electrical stimulation of the tongue and the lingual nerve. Electrical stimulation of the distal cut ends of the glossopharyngeal nerve root and inferior alveolar nerve caused the vasodilator and vasoconstrictor responses, whereas stimulation of the tongue and the proximal cut ends of the lingual nerve did not elicit the vasoconstrictor response. These results suggest that reflex vasodilatation in the cat mandibular division is exclusively mediated via activation of the parasympathetic nerve fibers, and that selective excitation of the parasympathetic nerve fibers in the oral area is possible.

Vasodilator responses following intracranial stimulation of the trigeminal, facial and glossopharyngeal nerves in the cat gingiva

The effects of electrical stimulation of the trigeminal, facial and glossopharyngeal nerves on gingival blood flow in the cat were studied. The intracranial part of these nerves was stimulated electrically, and gingival blood flow was measured by the laser Doppler technique. Electrical stimulation of the trigeminal, facial and glossopharyngeal nerves caused blood flow to increase in the ipsilateral gingiva both with the cranial nerve intact and after cutting it to the medulla. Stimulation of the distal cut ends of the facial and glossopharyngeal nerves elicited an increase in blood flow but no increase in systemic blood pressure. Pretreatment with hexamethonium reduced the increase in blood flow elicited by electrical stimulation of the facial and glossopharyngeal nerves, but had no effect on that elicited by stimulation of the trigeminal nerve. In contrast, pretreatment with tripelennamine attenuated the trigeminal nerve-stimulated blood flow increase, but not that elicited by stimulation of the facial and glossopharyngeal nerves. Atropine, propranolol and phentolamine had no effect on these responses. These results suggest that the autonomic nervous system, particularly the parasympathetic nervous system, is responsible for the blood flow increase elicited by facial and glossopharyngeal nerve stimulation, and that the trigeminal nerve-stimulated blood flow increase is induced by antidromic vasodilatation of the trigeminal sensory nerve.

Parasympathetic innervation of cutaneous blood vessels examined by retrograde tracing in the rat lower lip

The origin of vasoactive intestinal polypeptide (VIP)-immunoreactive and acetylcholinesterase (AChE)-positive perivascular nerve fibers in the lower lip of rats was investigated using the retrograde tracer, wheat germ agglutinin conjugated to enzymatically inactive horseradish peroxidase gold complex (WGAapoHRP-Au), in combination with immunohistochemistry and enzyme histochemistry, by comparing the cells of origin of projection to the parotid gland. After the application of the tracer to the lip, small- to medium-sized nerve cells were labelled exclusively in the ipsilateral otic ganglion. Most of them showed moderate VIP-immunoreactivity and AChE activity. In contrast, injection into the parotid gland resulted in labelling of mostly large-sized cells of the otic ganglion which showed intense VIP-immunoreactivity and AChE activity. These results confirmed that the parasympathetic innervation of the rat lip originates from the otic ganglion. It was further suggested that there are at least two subpopulations in the otic ganglion cells, different from each other in size and in VIP-immunoreactivity, which separately innervate the salivary gland and the blood vessels.

Postnatal development of autonomic and sensory innervation of thoracic hairy skin in the rat. A histochemical, immunocytochemical, and radioenzymatic study

Histochemical, immunocytochemical, and radioenzymatic techniques were used to examine the neurotransmitter-related properties of the innervation of thoracic hairy skin in rats during adulthood and postnatal development. In the adult, catecholamine-containing fibers were associated with blood vessels and piloerector muscles, and ran in nerve bundles throughout the dermis. The distribution of tyrosine hydroxylase (TH)-immunoreactive (IR) fibers was identical. Neuronal fibers displaying neuropeptide Y (NPY) immunoreactivity were seen in association with blood vessels. Double-labeling studies suggested that most, if not all, NPY-IR fibers were also TH-IR and likewise most, if not all, vessel-associated TH-IR fibers were also NPY-IR. Calcitonin gene-related peptide (CGRP)-IR fibers were observed near and penetrating into the epidermis, in close association with hair follicles and blood vessels, and in nerve bundles. A similar distribution of substance P (SP)-IR fibers was evident. In adult animals treated as neonates with the sympathetic neurotoxin 6-hydroxydopamine, a virtual absence of TH-IR and NPY-IR fibers was observed, whereas the distribution of CGRP-IR and SP-IR fibers appeared unaltered. During postnatal development, a generalized increase in the number, fluorescence intensity, and varicose morphology of neuronal fibers displaying catecholamine fluorescence, NPY-IR, CGRP-IR, and SP-IR was observed. By postnatal day 21, the distribution of the above fibers had reached essentially adult levels, although the density of epidermal-associated CGRP-IR and SP-IR fibers was significantly greater than in the adult. The following were not evident in thoracic hairy skin at any timepoint examined: choline acetyltransferase activity, acetylcholinesterase histochemical staining or immunoreactivity, fibers displaying immunoreactivity to vasoactive intestinal peptide, cholecystokinin, or leucine-enkephalin. The present study demonstrates that the thoracic hairy skin in developing and adult rats receives an abundant sympathetic catecholaminergic and sensory innervation, but not a cholinergic innervation.

Target-related patterns of co-existence of neuropeptide Y, vasoactive intestinal peptide, enkephalin and substance P in cranial parasympathetic neurons innervating the facial skin and exocrine glands of guinea-pigs

The patterns of co-existence of neuropeptides in cranial autonomic neurons of guinea-pigs have been examined with quantitative double-labelling immunofluorescence and retrograde axonal tracing using Fast Blue. Within the sphenopalatine, otic, sublingual and submandibular ganglia, and a prominent intracranial ganglion associated with the glossopharyngeal nerve, most neurons contained immunoreactivity of vasoactive intestinal peptide, neuropeptide Y, enkephalin and substance P in combinations that were correlated with their projections. Hair follicles in the facial skin formed a major target of sphenopalatine ganglion cells. The combinations of peptides co-existing in these neurons depended upon the region of the skin where the follicles were located. The parotid gland was innervated by neurons with cell bodies in the otic ganglion or the intracranial ganglion. Most of these neurons contained immunoreactivity to all four peptides. The sublingual gland was innervated by local ganglion cells usually containing immunoreactivity to neuropeptide Y, vasoactive intestinal peptide and substance P. The submandibular gland was innervated by local ganglion cells containing enkephalin immunoreactivity and low levels of immunoreactivity to neuropeptide Y. Presumptive vasodilator neurons, containing immunoreactivity to vasoactive intestinal peptide but no other peptide examined here, comprised less than 10% of cranial autonomic ganglion cells. These results demonstrate that the patterns of co-existence of neuropeptides in cranial autonomic neurons show a high degree of target specificity. The discovery that hair follicles form a major parasympathetic target implies a broader range of actions of cranial autonomic neurons than has been suspected until now.

VIP: molecular biology and neurobiological function

In the mammalian brain, a major regulatory peptide is vasoactive intestinal peptide (VIP). This 28 amino acid peptide, originally isolated from the porcine duodenum, was later found in the central and peripheral nervous systems and in endocrine cells, where it exhibits neurotransmitter and hormonal roles. Increasing evidence points to VIP's importance as a mediator or a modulator of several basic functions. Thus, VIP is a major factor in brain activity, neuroendocrine functions, cardiac activity, respiration, digestion, and sexual potency. In view of this peptide's importance, the mechanisms controlling its production and the pathways regulating its functions have been reviewed. VIP is a member of a peptide family, including peptides such as glucagon, secretin, and growth hormone releasing hormone. These peptides may have evolved by exon duplication coupled with gene duplication. The human VIP gene contains seven exons, each encoding a distinct functional domain on the protein precursor or the mRNA. VIP gene transcripts are mainly found in neurons or neuron-related cells. VIP gene expression is regulated by neuronal and endocrine signals that contribute to its developmental control. VIP exerts its function via receptor-mediated systems, activating signal transduction pathways, including cAMP. It can act as a neurotransmitter, neuromodulator, and a secretagog. As a growth and developmental regulator, VIP may have a crucial effect as a neuronal survival factor. We shall proceed from the gene to its multiple functions.

Peripheral patterns of calcitonin-gene-related peptide general somatic sensory innervation: cutaneous and deep terminations

The distribution of calcitonin-gene-related peptide (CGRP) immunoreactivity (IR) was studied in peripheral tissues of rats. The ganglionic origin, somatosensory nature, and anatomic relations of this thin-axon population were evaluated with particular emphasis on possible nociceptive roles. In animals untreated with colchicine, CGRP-IR is found in a vast proportion of small- and medium-diameter sensory ganglion cells that give rise to numerous thinly myelinated and unmyelinated axons that display CGRP-IR throughout the body. The integumentary innervation consists, in part, of an extensive subpapillary network largely traced to dermal blood vessels, sweat glands, and "free" nerve endings, some of which are found within regions containing only mast cells, fibroblasts, and collagen. Dermal papillae contain CGRP-IR axons surrounding each vascular loop; other papillary axons end freely or occasionally surround Meissner corpuscles. Intraepithelial axons enter glabrous epidermal pegs, branching and exhibiting terminals throughout the stratum spinosum. A similar pattern is found in hairy skin with additional innervation entering the base and surrounding the lower third of each hair follicle, but apparently not supplying sebaceous glands and arrector pili muscle. Axons innervating nonkeratinized oral epithelium are similar or greater in number and distribution compared to epidermis, often with more extensive branching. The high density of intraepithelial CGRP-IR innervation does not appear to correlate with the sensitive mechanoreceptor-based increase in spatial sensory discriminative capacities in the distal portions of the limb. In deep somatic tissues, CGRP-IR is principally related to vasculature and motor end plates of striated muscle, but there is an extensive network of thin axons within bone, principally in the periosteum, and focally in joint capsules, but not in relation to muscle spindles or tendon organs. These findings, together with the distribution in cranial tissues described in an accompanying paper (Silverman and Kruger: J. Comp. Neurol. 280:303-330, '89), are considered in the context of a "noceffector" concept incorporating the efferent role of these sensory axons in various tissues. It is suggested that involvement in tissue maintenance and renewal during normal function, as well as following injury, may predominate over the relatively infrequent nociceptive role of this peptidergic sensory system.