Plasticity in expression of co-transmitters and autonomic nerves in aging and disease

Aging and total stenosis triggers differential responses of carotid and basilar arteries to endothelin-1 and phenylephrine

Our aim was to investigate the effects of ageing on the vascular contractility of carotid and basilar arteries from guinea-pigs, in a model of total stenosis. Moreover, we attempted to identify whether total stenosis of the left common carotid (stenosed) in adult guinea-pigs, would affect the contractions of contralateral carotid (intact) and basilar arteries to different vasoconstrictors. With this purpose, the left carotid was occluded with a silk thread at a position close to its origin. Vascular reactivity experiments using standard muscle bath were performed 7, 15, 30, and 90 days after carotid occlusion. Reactivity of carotid and basilar arteries to endothelin-1, phenylephrine and KCl was reduced with ageing in naive guinea-pigs. The endothelin-1 and KCl-induced contractions were unaltered in arteries from SHAM-operated animals. Moreover, phenylephrine-induced contractions were reduced in both carotids from 7 days SHAM-operated guinea-pigs, when compared to naive group. Stenosis induced progressive reduction in the contraction induced by endothelin-1, phenylephrine and KCl in the stenosed carotid, when compared to their respective age-matched naive and SHAM groups. Interestingly, an increased contractile-response to vasoconstrictor agents in all the contralateral carotids was observed. Stenosis (30 and 90 days) also induced an increase in the contractions induced by endothelin-1 in the basilar artery. Conversely, phenylephrine and KCl-induced contractions were reduced in basilar arteries 7, 15, 30 and 90 days after stenosis. These results showed that stenosis in adult guinea-pigs induce alterations of vascular reactivity in arteries distant from the site of injury. Thus, in spite of the common use of contralateral carotid as control, it must be aware of the potential alteration induced by stenosis in the vascular motility of such vessels. Additionally, it was verified a relationship between the period of stenosis and the alterations in the vascular reactivity to these vasoconstrictors.

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.

Contractility of urinary bladder and vas deferens after sensory denervation by capsaicin treatment of newborn rats

1. Capsaicin, a selective sensory neurotoxin, was given to newborn rats and at the age of 3 months the contractile activity of the urinary bladder detrusor muscle and vas deferens evoked by either electrical field stimulation (EFS) or exogenous adenosine 5'-triphosphate (ATP) and carbachol (urinary bladder), or ATP and noradrenaline (vas deferens) were tested. 2. EFS of the urinary bladder evoked contractions which consisted of cholinergic and purinergic components, since they could be partially blocked by either the muscarinic cholinoceptor antagonist, atropine (0.3 microM) or by desensitization of P2x-purinoceptors with alpha,beta-methylene ATP (10 microM). In capsaicin-treated rats, contractions of the urinary bladder evoked by EFS were significantly larger than those of control (vehicle-treated) animals, and this difference remained after the purinergic component of the contractions was blocked by desensitization of P2x-purinoceptors with alpha,beta-methylene ATP. However, when the cholinergic component of the contractions was blocked with atropine, the difference between the groups at 8 Hz and 16 Hz was abolished; EFS caused significantly larger contractions of the capsaicin-treated rat bladder only at frequencies of 2 Hz and 4 Hz. 3. EFS evoked contractions of the vas deferens consisted of adrenergic and purinergic components since they could be partially blocked by either the alpha-adrenoceptor antagonist, phentolamine (3 microM) or by alpha,beta-methylene ATP (10 microM). The contractions of the vas deferens were significantly larger than in the capsaicin-treated rats only at a frequency of 16 Hz. There were no differences between vas deferens contractions of the two groups either after desensitization of P2X-purinoceptors by alpha,beta-methylene ATP or in the presence of phentolamine.4. Contractions of the capsaicin-treated rat urinary bladder evoked by exogenous carbachol (0.1-100 microM) were not significantly different from those of controls, the pD2 values being 1.78 +/- 0.23 micro M and 1.90 +/- 0.20 micro M respectively. There was also no significant difference between the groups in contractions of the bladder evoked by ATP (10 micro M-3 mM).5. Contractions of the vas deferens evoked by either ATP (10 micro M-3 mM) or noradrenaline (1-1000 micro M) in the capsaicin-treated group showed no significant difference between control and capsaicin treated rats.6. In conclusion, the present results indicate that chronic capsaicin treatment increases the amplitude of contractions of the rat urinary bladder, an effect which preferentially involves the cholinergic component of the response; since the response to carbachol is unaffected, the change involves prejunctional mechanisms. In contrast, both the purinergic and adrenergic components of contraction in the vas deferens are unaffected by capsaicin. It is suggested that sensory nerves have a trophic influence on the development of parasympathetic nerves in the rat bladder; removal of sensory nerves shortly after birth results in an increase mainly in the cholinergic, and to a lesser extent purinergic component.

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

The sensory nerves, containing substance P and calcitonin gene-related peptide, and noradrenaline-containing sympathetic nerves of the rat uterus were analyzed following long-term sympathectomy with guanethidine in prepubertal (four weeks), young adult (eight weeks) and fully adult animals (18 weeks). Immunohistochemical and histochemical methods were used in association with nerve density measurements and biochemical assays. The main findings were as follows: (1) long-term guanethidine treatment completely abolished the noradrenergic innervation of the uterine horn and parametrial tissue and markedly reduced the tissue levels of noradrenaline in both regions at the three ages analysed; (2) in the uterine horn guanethidine treatment had no effect on the tissue levels of either calcitonin gene-related peptide or substance P or on the density of calcitonin gene-related peptide-containing nerves, at any of the three ages studied; (3) in the parametrial tissue increased levels of calcitonin gene-related peptide were observed at 8 and 18 weeks of age, together with a significant increase in the density of calcitonin gene-related peptide-containing nerves. Substance P levels showed a transient increase in this tissue at eight weeks. In conclusion, long-term sympathectomy with guanethidine resulted in an increase in calcitonin gene-related peptide and substance P in sensory nerves in the parametrial tissue, but not in the uterine horn. The changes in the parametrial tissue only occurred after puberty. It is suggested that sensory nerves in the uterine horn may be less responsive to sympathetic denervation since loss of sympathetic nerves occurs as part of a normal physiological process during pregnancy in this region.

Maturational changes in sympathetic and sensory innervation of the rat uterus: effects of neonatal capsaicin treatment

The plasticity of the sympathetic and sensory innervation of the rat uterus was examined, before and after puberty, in controls and in animals where primary sensory nerves had been destroyed by neonatal capsaicin treatment. Immunohistochemical and histochemical methods were used in association with nerve density measurements and biochemical assays. The main findings were as follows: (1) Puberty was associated with a marked increase in the weight of the uterine horn, uterine cervix and parametrial tissue. This was unaffected by capsaicin treatment. (2) The sympathetic innervation of the uterine horn and parametrial tissue was reduced following puberty as revealed by a decrease in the density of noradrenaline-containing nerves and a marked decrease in the tissue concentration of noradrenaline. Sympathetic nerves supplying the uterine cervix and the blood vessels of the uterus appeared to be unaffected by puberty. (3) In contrast, the sensory supply of the uterus by substance P and calcitonin gene-related peptide-containing nerves increased in parallel with uterine growth during puberty resulting in no change in nerve density and only a slight reduction in peptide concentration. (4) Neonatal capsaicin treatment caused a long-lasting depletion of substance P- and calcitonin gene-related peptide-containing nerves. In the uterine horn and parametrial tissue, capsaicin-resistant calcitonin gene-related peptide, but not substance P, still increased with tissue weight during puberty, indeed, in the uterine horn, the relative increase was greater than in controls. (5) Sensory denervation resulted in an increase in the non-vascular sympathetic supply of the uterus, although there was a regional variation in the time course of the response. Perivascular sympathetic nerves were unaffected by capsaicin treatment. The pattern of change in non-vascular noradrenaline-containing nerves associated with puberty was similar in nature to controls. Thus, there is considerable plasticity in the innervation of the uterus both during puberty and following sensory denervation. A complex pattern of change occurs with differential responses in vascular and nonvascular nerves and in different regions of the uterus. Such differences may be due in part to the different origins of individual nerve populations and/or to their relative sensitivities to sex hormones.