Plasticity of autonomic nerves: differential effects of long-term guanethidine sympathectomy on the sensory innervation of the rat uterus during maturation

The Influence of an Adrenergic Antagonist Guanethidine (GUA) on the Distribution Pattern and Chemical Coding of Dorsal Root Ganglia (DRG) Neurons Supplying the Porcine Urinary Bladder

Although guanethidine (GUA) was used in the past as a drug to suppress hyperactivity of the sympathetic nerve fibers, there are no available data concerning the possible action of this substance on the sensory component of the peripheral nervous system supplying the urinary bladder. Thus, the present study was aimed at disclosing the influence of intravesically instilled GUA on the distribution, relative frequency, and chemical coding of dorsal root ganglion neurons associated with the porcine urinary bladder. The investigated sensory neurons were visualized with a retrograde tracing method using Fast Blue (FB), while their chemical profile was disclosed with single-labeling immunohistochemistry using antibodies against substance P (SP), calcitonin gene-related peptide (CGRP), pituitary adenylate cyclase activating polypeptide (PACAP), galanin (GAL), neuronal nitric oxide synthase (nNOS), somatostatin (SOM), and calbindin (CB). After GUA treatment, a slight decrease in the number of FB⁺ neurons containing SP was observed when compared with untreated animals (34.6 ± 6.5% vs. 45.6 ± 1.3%), while the number of retrogradely traced cells immunolabeled for GAL, nNOS, and CB distinctly increased (12.3 ± 1.0% vs. 7.4 ± 0.6%, 11.9 ± 0.6% vs. 5.4 ± 0.5% and 8.6 ± 0.5% vs. 2.7 ± 0.4%, respectively). However, administration of GUA did not change the number of FB⁺ neurons containing CGRP, PACAP, or SOM. The present study provides evidence that GUA significantly modifies the sensory innervation of the porcine urinary bladder wall and thus may be considered a potential tool for studying the plasticity of this subdivision of the bladder innervation.

[Regulatory mechanisms of calcitonin gene-related peptide (CGRP) in skin inflammation]

Skin inflammation is one of several allergic symptoms that are regulated by several mediator molecules. One of these molecules, calcitonin gene-related peptide (CGRP) affects several immune cells including T cells, B cells, dendiritic cells and mast cells. CGRP binds to CGRP receptors composed of receptor activity-modifying protein 1 (RAMP1) and calcitonin receptor-like receptor (CLR) to modulate various functions such as pain transmission and vasodilation. Studies showing that CGRP physiologically regulates skin inflammation using a CGRP antagonist, capsaicin-induced depletion model, RAMP1-deficient mice and mouse contact hypersensitivity (CHS) model have been reported. Interestingly, while CGRP has inhibitory effects on Th1-mediated CHS, it was demonstrated that CGRP enhances Th2-mediated CHS response. Moreover, these skin inflammations were affected by elevated CGRP concentrations through an abnormal condition of the nervous system induced by exposure to psychological stress or neonatal chemical stimulation. In this review, we present the importance of CGRP in the regulation of skin inflammation under the several nervous conditions and provide a new insight into understanding various types of skin inflammation and skin diseases.

Neuroendocrine pathway involvement in the loss of the cutaneous pressure-induced vasodilatation during acute pain in rats

Pain is regarded as a risk factor in pressure ulcer development by contributing to immobility. Pressure-induced vasodilatation (PIV) is a mechanism whereby cutaneous blood flow increases in response to progressive locally applied pressure, thereby delaying the occurrence of ischaemia and appearing to be a protective response to local pressure. When the interaction between nervous and vascular systems is deregulated, PIV, which relies on both systems, is absent. We thus hypothesized that acute pain could alter PIV. This study investigated the effects on PIV of acute pain triggered by noxious heat (50 degrees C) applied to the tail of anaesthetized rats. To address the mechanisms underlying these effects, chronic sympathectomy was performed using guanethidine, and the plasma concentrations of pituitary adrenocorticotrophin (ACTH) and catecholamines were measured. Our results show that acute pain induces a loss of PIV associated with an increase of ACTH. Direct involvement of hypertensive effects and peripheral sympathetic nervous system are excluded in the loss of PIV, whereas the activation of brain structures that have descending inhibitory control cannot be excluded. A low dose of systemic morphine prevented this loss of PIV and maintained the ability of the cutaneous microcirculation to adapt to the applied pressure. The loss of a protective response to local pressure (PIV) induced by acute pain lends physiological support to the direct involvement of pain in pressure ulcer development. Therefore, an adequate evaluation and treatment of pain is crucial.

Calcitonin gene-related peptide and substance P contribute to reduced blood pressure in sympathectomized rats

CGRP and substance P (SP) are produced in dorsal root ganglia (DRG) sensory neurons and modulate vascular tone. Sympathetic and sensory nerves compete for NGF, a potent stimulator of CGRP and SP, and it has been suggested that sympathetic hyperinnervation in spontaneously hypertensive rats may reduce the availability of NGF to sensory nerves, thus reducing CGRP and SP. The purpose of this study was to determine whether destruction of peripheral sympathetic nerves in normal rats would increase the availability of NGF for sensory neurons and enhance expression of CGRP and SP. Sympathectomy was produced in rats by guanethidine sulfate administration. Control rats received saline. Sympathectomized rats displayed reductions in blood pressure (BP) and atria norepinephrine levels, whereas NGF levels in the DRG, spleen, and ventricles were increased. Sympathectomy also enhanced CGRP and SP mRNA and peptide content in DRG. Administration of CGRP and SP receptor antagonists increased the BP in sympathectomized rats but not in the controls. Thus sympathectomy enhances sensory neuron CGRP and SP expression that contributes to the BP reduction.

Effects of functional peripheral sympathetic denervation induced by guanethidine on follicular development and ovulation of the adult female guinea pig

The present study investigates the effects of functional sympathetic peripheral denervation induced by guanethidine sulphate (GTD) to adult female guinea pigs in the follicular (FPh) or luteal phases (LPh) on their oestrous cyclicity and ovulation. No differences were observed in oestrous cyclicity or the average number of corpora lutea present in the ovaries between the control and denervated animals. Guanethidine sulphate administration resulted in a significant decrease in ovarian norepinephrine content, higher for the left ovary than for the right one. Serum oestrogen and progesterone concentrations, the mean of follicles, and its diameter were different, depending on the oestral cycle in which the treatment was performed. These results suggest that in adult normal female guinea pigs, ovarian innervation participates in the regulation of follicular development in an inhibitory way.

Effects of infantile/prepubertal chronic estrogen treatment and chemical sympathectomy with guanethidine on developing cholinergic nerves of the rat uterus

The innervation of the uterus is remarkable in that it exhibits physiological changes in response to altered levels in the circulating levels of sex hormones. Previous studies by our group showed that chronic administration of estrogen to rats during the infantile/prepubertal period provoked, at 28 days of age, an almost complete loss of norepinephrine-labeled sympathetic nerves, similar to that observed in late pregnancy. It is not known, however, whether early exposure to estrogen affects uterine cholinergic nerves. Similarly, it is not known to what extent development and estrogen-induced responses in the uterine cholinergic innervation are affected by the absence of sympathetic nerves. To address this question, in this study we analyzed the effects of infantile/prepubertal chronic estrogen treatment, chronic chemical sympathectomy with guanethidine, and combined sympathectomy and chronic estrogen treatment on developing cholinergic nerves of the rat uterus. Cholinergic nerves were visualized using a combination of acetylcholinesterase histochemistry and the immunohistochemical demonstration of the vesicular acetylcholine transporter (VAChT). After chronic estrogen treatment, a well-developed plexus of cholinergic nerves was observed in the uterus. Quantitative studies showed that chronic exposure to estrogen induced contrasting responses in uterine cholinergic nerves, increasing the density of large and medium-sized nerve bundles and reducing the intercept density of fine fibers providing myometrial and perivascular innervation. Estrogen-induced changes in the uterine cholinergic innervation did not appear to result from the absence/impairment of sympathetic nerves, because sympathectomy did not mimic the effects produced by estrogen. Estrogen-induced responses in parasympathetic nerves are discussed, considering the direct effects of estrogen on neurons and on changes in neuron-target interactions.

The evaluation of sympathetic system-related contractile activity of the rat vas deferens after ligation and intra-abdominal placement of the testis

OBJECTIVE

To evaluate the contractile response of the vas deferens in a model of stress, to determine any changes in sympathetic activity as a result of stress in the ipsilateral testis, which decreases blood flow to the contralateral testis.

MATERIALS AND METHODS

The study comprised two groups of six rats each; group 1 underwent a sham operation, and in group 2 the right testis was placed into the abdominal cavity and the vas deferens ligated. After 30 days, the vasa deferentia were resected bilaterally and their isometric contractions recorded. Electrical-field stimulation (EFS) was applied through a pair of platinum electrodes and concentration-response curves constructed for noradrenaline at 37 degrees C and to a solution containing 80 mmol/L K+.

RESULTS

The vasa deferentia in both groups showed similar contractile responses to EFS, which were frequency-dependent and maximal at 80 Hz. Noradrenaline-induced contractile activity was lower in amplitude in the vasa deferentia of group 2 than in the contralateral and ipsilateral vasa deferentia of group 1, which were not significantly different from each other. All groups responded similarly to high K+.

CONCLUSION

Intra-abdominal placement of the testes with vas deferens ligation decreased the contractile response to noradrenaline in the ipsilateral vas deferens without altering the contractile response to EFS and high K+. This difference could be caused by a reduction in the number of postjunctional alpha-adrenergic receptors or decreased receptor sensitivity. Both possibilities suggest that the vas deferens may initiate sympathetic activity, which may be responsible for contralateral testicular deterioration.

Neurogenic and non-neurogenic responses in the urinary bladder of hibernating hamster

1. Purinergic and cholinergic components of parasympathetic neurotransmission and contractile responses to exogenous alpha,beta-methylene ATP, acetylcholine, substance K, substance P, calcitonin gene-related peptide, vasoactive intestinal polypeptide and capsaicin have been investigated in the urinary bladder of hibernating hamsters (4 weeks), cold exposed (4 weeks) and age-matched controls. 2. Electrical field stimulation (EFS) evoked increased frequency-dependent contractions in the detrusor strips from hibernating hamsters compared with those obtained from cold-exposed and age-matched animals. Tetrodotoxin (10(-6) M) completely blocked the frequency-dependent contractions in all groups. 3. The purinergic component of the parasympathetic neurotransmission was not affected in hibernating and cold-exposed animals while the cholinergic component was increased with respect to age-matched animals. The neurogenic response to EFS, still present after incubation with atropine (10(-6) M) and suramin (10(-4) M), was attenuated by indomethacin (10(-6) M) and blocked by tetrodotoxin (10(-6) M). 4. Exogenous administration of alpha,beta-methylene ATP elicited a significantly reduced contraction in strips from hibernating and cold-exposed hamsters relative to age-matched animals. The contractile response to exogenous acetylcholine was greater in the detrusors from hibernating hamsters than in cold-exposed and age-matched animals. Substance K elicited reduced contractions in preparations from hibernating animals compared with cold-exposed and control animals. Calcitonin gene-related peptide, vasoactive intestinal polypeptide, substance P and capsaicin did not elicit any relaxant or contractile response either at resting tone or in carbachol (5 x 10(-7) M)-precontracted tissues. 5. In summary, our findings indicate that 4 weeks of hibernation can significantly increase neurogenic responses in the hamster urinary bladder. This appears to be due to an increase in postjunctional responses to acetylcholine. In contrast, there was a decrease of the postjunctional responses to the parasympathetic cotransmitter ATP and also to the sensory-motor neurotransmitter substance K.

Expression of beta-adrenergic receptors in the rat uterus: effects of puberty and oestrogen treatment during prepubertal development

The expression of beta-adrenoceptors in the rat uterus has been analysed during the peripubertal transition and following acute and chronic oestradiol treatment during prepubertal development. The distribution and density of beta-adrenoceptors was assessed autoradiographically on cryostat tissue sections using [3H]-dihydroalprenolol ([3H]-DHA). Binding sites were localised in all ages and experimental situations examined and showed the following intensity of labelling: endometrial epithelium > longitudinal muscle layer > circular myometrial layer > endometrial stroma. Competition experiments with the selective antagonists ICI 118,551 and atenolol, showed that most of the beta-adrenoceptors in the uterus belong to the beta(2) receptor subclass. In prepubertal animals, the density of [3H]-DHA binding sites was extremely low. Following puberty the density of binding sites showed a generalised increase. Acute administration of oestradiol at the end of the prepubertal period provoked an increase in the density of [3H]-DHA binding sites in all uterine regions, but the levels of labelling were lower than in peripubertal animals at proestrus and oestrus. Following chronic oestrogen treatment during postnatal development, oestradiol increased further the density of [3H]-DHA binding sites. Results are discussed considering both the endocrine and neural changes accompanying puberty and oestradiol treatment.

Plasticity in adult and ageing sympathetic neurons

The nature of neural plasticity and the factors that influence it vary throughout life. Adult neurons undergo extensive and continual adaptation in response to demands that are quite different from those of early development. We review the main influences on the survival, growth and neurotransmitter expression in adult and ageing sympathetic neurons, comparing these influences to those at work in early development. This "developmental" approach is proposed because, despite the contrasting needs of different phases of development, each phase has a profound influence on the mechanisms of plasticity available to its successors. Interactions between neurons and their targets, whether effector cells or other neurons, are vital to all of these aspects of neural plasticity. Sympathetic neurons require access to target-derived diffusible neurotrophic factors such as NGF, NT3 and GDNF, as well as to bound elements of the extracellular matrix such as laminin. These factors probably influence plasticity throughout life. In adult life, and even in old age, sympathetic neurons are relatively resistant to cell death. However, they continue to require target-derived diffusible and bound factors for their maintenance, growth and neurotransmitter expression. Failure to maintain appropriate neuronal function in old age, for example in the breakdown of homeostasis, may result partly from a disturbance of the dynamic, trophic relationship between neurons and their targets. However, there is no clear evidence that this is due to a failure of targets to synthesize neurotrophic factors. On the neural side of the equation, altered responsiveness of sympathetic neurons to neurotrophic factors suggests that expression of the trk and p75 neurotrophin receptors contributes to neuronal survival, maintenance and growth in adulthood and old age. Altered receptor expression may therefore underlie the selective vulnerability of some sympathetic neurons in old age. The role of neural connectivity and activity in the regulation of synthesis of target-derived factors, as well as in neurotransmitter dynamics, is reviewed.

Age-related changes in purinergic and adrenergic components of sympathetic neurotransmission in guinea-pig seminal vesicles

1. Purinergic and adrenergic components of sympathetic neurotransmission and contractile responses to exogenous alpha,beta-methylene ATP and noradrenaline have been investigated in the seminal vesicles of 1-day (new-born), 2-weeks (young), 12-weeks (adult) and 2-years old (aged) guinea-pigs. 2. In seminal vesicles of new-born guinea-pigs electrical field stimulation (EFS; 80 V, 0.5 ms for 30 s, 2-32 Hz) evoked tonic frequency-related contractions. In 2-weeks old guinea-pigs the tonic contraction masked an initial phasic component of the neurogenic responses, whereas in 12-weeks and 2-years old guinea-pigs, neurogenic responses were biphasic, a phasic response being followed by a tonic contraction. In all experimental groups, prazosin (10(-6) M) blocked the tonic contraction while desensitization of P2X receptors by alpha,beta-methylene ATP (10(-4) M) abolished the phasic responses. 3. The phasic purinergic component of the neurogenic response was significantly higher in 12-weeks and 2-years old animals, compared with 2-weeks old guinea-pigs. At 32 Hz phasic contractions were (mN mg(-1) tissue): 0.047+/-0.012, 0.018+/-0.040 and 0.147+/-0.026 in 2-weeks, 12-weeks and 2-years old guinea-pigs, respectively. In contrast, the tonic adrenergic component of the neurogenic contraction significantly declined at 12-weeks and 2-years compared with 2-weeks old guinea-pigs. 4. Contractile responses (mN mg(-1) tissue) to the highest concentration of alpha,beta-methylene ATP tested were significantly higher in 2-weeks (0.248+/-0.022) than in 1-day old animals (0.113+/-0.012) and decreased in 12-weeks (0.163+/-0.016) and 2-years old guinea-pigs (0.200+/-0.008). The pD2 values for the purinoceptor agonist were also significantly lower in adult (4.74+/-0.20) and aged guinea-pigs (5.22+/-0.08) compared with 2-weeks old animals (5.91+/-0.27). Conversely, responses to the highest concentration of noradrenaline gradually decreased with age, without significant changes in the pD2 values. Contractile responses to KCl (240 mM) did not differ significantly between the experimental groups. 5. These results demonstrate age-related changes in purinergic and adrenergic components of sympathetic neurotransmission in the guinea-pig seminal vesicles. The purinergic component is absent in new-born animals and it appears fully developed in adult and old guinea-pigs, while the adrenergic component decreases with age. Pre- and postjunctional mechanisms contributing to the age-related changes of sympathetic neurotransmission are discussed.

Development and maturation of noradrenaline-containing nerves of the rat uterine artery. Effects of acute and chronic oestrogen treatment

The development and maturation of noradrenaline-containing nerves of the rat uterine artery was investigated, histochemically and biochemically, at seven different postnatal age-stages and following acute and chronic treatment with oestradiol. Morphological changes in the vessel were quantitatively evaluated on Toluidine Blue-stained semithin sections and low magnification electronmicrographs. In summary, the uterine artery is innervated at birth; the adult pattern of innervation is established at two weeks of age; the innervation density increases progressively between the infantile and prepubertal periods, accompanying proliferation and growth of smooth muscle cells in the tunica media; changes in the innervation are followed by an increase in the tissue concentration of noradrenaline and neither the endocrine changes characterizing puberty nor acute or chronic treatment with oestradiol have an effect on the pattern of development of the uterine artery and associated noradrenaline-containing nerves. Results are interpreted considering the differential susceptibility of urinogenital organs to sex hormones.

Effect of celiac ganglionectomy on tachykinin innervation, receptor distribution and intestinal responses in the rat

Substance P (SP) is an important neurotransmitter in the control of intestinal motility and is found in both the enteric and sympathetic nervous systems. This study examined the effect of celiac ganglionectomy on (1) mechanical properties of the circular muscles of the duodenum, ileum and proximal colon, (2) circular muscle responses to SP and neurokinin A. (3) distribution of substance P-like immunoreactive nerves, and (4) the distribution of neurokinin 1 and neurokinin 2 receptors. Celiac ganglionectomy resulted in an effective sympathectomy as evidenced by a marked decrease in norepinephrine content and tyrosine hydroxylase staining in the duodenum, ileum and proximal colon. The in vitro length/tension characteristics of the circular muscle of the duodenum, ileum and colon were unchanged after ganglionectomy. In all regions of the gut studied, substance P and neurokinin A caused dose-dependent contractions that were unaltered by celiac ganglionectomy. Immunohistochemistry revealed moderate substance P-like immunoreactive fibers in the myenteric plexus, submucosal plexus and circular muscle of the ileum, while in the colon, substance P-like immunoreactivity was intense in the myenteric plexus, and moderate in the circular muscle. In vitro autoradiography showed minimal binding of SP (NK1 receptor) or neurokinin A (NK2 receptor) in the ileum and significantly greater binding in the circular muscle layer of the colon. Celiac ganglionectomy did not affect substance P-like immunoreactivity, or NK1 or NK2 receptor binding. A greater contractile response to neurokinins was seen in the colon than in the duodenum or ileum, which paralleled the receptor density. The studies demonstrate that surgical celiac ganglionectomy, unlike chemical sympathectomy, does not affect the substance P innervation, receptor density or physiological responses of the intestine. The greater contractile response of the colon than the ileum parallels the greater receptor density rather than the peptide content as determined by immunhistochemistry.

Effects of chronic and acute oestrogen treatment on the developing noradrenaline-containing nerves of the rat uterus

The developing noradrenaline-containing (NA-C) sympathetic nerves of the rat uterus were analyzed following acute and chronic treatment with oestrogen. Histochemical methods were used in association with nerve density measurements and biochemical assays. For comparative purposes, noradrenaline (NA) levels were measured in the urinary bladder and right auricle following chronic oestrogen treatment. Acute treatment was performed by s.c. administration of a single dose of 40 micrograms oestradiol cypionate on the 25th day of age. Chronic treatment consisted of four doses of 10 micrograms oestradiol on days 10, 15, 20 and 25 of postnatal development. Both acute- and chronic-treated animals were killed at 28 days of age. The main biochemical findings were the following: (a) both acute and chronic oestrogen treatment increased the weight of the uterine horn, parametrial tissue and uterine cervix; (b) in the uterine horn, the total content of NA was reduced following both oestrogen treatments. However, the degree of reduction was greater after chronic treatment; (c) in the parametrial tissue, the NA levels were reduced only after chronic treatment; (d) in the cervix, the NA total content was increased after both treatments; (e) in the urinary bladder, there was a parallel increase between organ growth and NA content following chronic oestrogen treatment; (e) in the auricle neither the tissue weight nor the total content of NA were changed by chronic estrogen treatment. Histochemical studies showed that: (a) acute treatment with one single dose of oestradiol, provoked a marked reduction in the density of NA-C nerves associated with the myometrial and parametrial smooth muscle, without affecting the innervation of blood vessels; (b) following chronic treatment, the only fibers we were able to recognize were those associated with blood vessels. These fibers were thinner and less intensely fluorescent than in controls. Results are interpreted considering the differential sensitivity of uterine nerves to sex hormones. A possible involvement of oestrogen in changes of noradrenergic innervation of the uterus following puberty is discussed.