Regulation of sympathetic trophic factors in smooth muscle

Development of the autonomic nervous system: a comparative view

In this review we summarize current understanding of the development of autonomic neurons in vertebrates. The mechanisms controlling the development of sympathetic and enteric neurons have been studied in considerable detail in laboratory mammals, chick and zebrafish, and there are also limited data about the development of sympathetic and enteric neurons in amphibians. Little is known about the development of parasympathetic neurons apart from the ciliary ganglion in chicks. Although there are considerable gaps in our knowledge, some of the mechanisms controlling sympathetic and enteric neuron development appear to be conserved between mammals, avians and zebrafish. For example, some of the transcriptional regulators involved in the development of sympathetic neurons are conserved between mammals, avians and zebrafish, and the requirement for Ret signalling in the development of enteric neurons is conserved between mammals (including humans), avians and zebrafish. However, there are also differences between species in the migratory pathways followed by sympathetic and enteric neuron precursors and in the requirements for some signalling pathways.

Generating diversity: Mechanisms regulating the differentiation of autonomic neuron phenotypes

Sympathetic and parasympathetic postganglionic neurons innervate a wide range of target tissues. The subpopulation of neurons innervating each target tissue can express unique combinations of neurotransmitters, neuropeptides, ion channels and receptors, which together comprise the chemical phenotype of the neurons. The target-specific chemical phenotype shown by autonomic postganglionic neurons arises during development. In this review, we examine the different mechanisms that generate such a diversity of neuronal phenotypes from the pool of apparently homogenous neural crest progenitor cells that form the sympathetic ganglia. There is evidence that the final chemical phenotype of autonomic postganglionic neurons is generated by both signals at the level of the cell body that trigger cell-autonomous programs, as well as signals from the target tissues they innervate.

Relative contribution of sympathetic and sensory nerves to thermal nociception and tissue trophism in rats

Neonatal injection of 6-hydroxydopamine (420 mg/kg s.c.) lowered thermal nociceptive threshold (hot plate and tail immersion tests) and increased levels of substance P-like immunoreactivity in the skin (paws, tail, area of vibrissae) of Wistar rats. Chemical ablation of primary afferents, induced in either neonatal or adult rats by systemic administration of capsaicin, increased thermal nociceptive threshold (hot plate), irrespective of 6-hydroxydopamine pretreatment, and reduced substance P-like immunoreactivity in the hind-paw skin of either control or sympathectomized rats. Capsaicin pretreatment of neonatal but not adult rats produced antinociceptive effect in the tail-immersion test and completely reversed the hyperalgesic effect of sympathectomy, without affecting levels of substance P-like immunoreactivity in the tail skin. These findings indicate that sympathetic nerves and different subsets of capsaicin-sensitive primary afferents are involved in the processing of thermal nociceptive input. Corneal and cutaneous lesions were induced by neonatal sensory denervation with capsaicin. Sympathectomy afforded protection against the development of corneal pathology, while it did not affect the occurrence of cutaneous lesions. It appears that a balance in the neuronal activity between sympathetic neurons and trigeminal sensory neurons is critical for maintaining the normal trophism of the cornea, and that sensory neuropeptides play a key role in the maintenance of normal trophism of the skin.

Extension of sympathetic neurites in vitro towards explants of embryonic and neonatal mouse heart and stomach: ontogeny of neuronotrophic factors

In order to establish when target organs first produce neuronotrophic factors, extension of neurites in vitro from sympathetic ganglia (superior cervical and coeliac) of 1-day neonatal mice towards explants of 10-, 11-, 14- and 17-day embryonic and 1-day neonatal atrium and stomach was examined in co-cultures. Longer neurites extended from ganglia towards, than away from, atrial targets at all stages examined, and was most marked towards 17-day embryonic and neonatal explants. Treatment of atrial co-cultures with antiserum to nerve growth factor (NGF) almost totally blocked preferential neurite outgrowth. Directional growth of neurites towards stomach explants in co-cultures was not as pronounced as that towards atrium; extension of neurites was most marked when stomach was provided by 11-, 14- and 17-day embryos. Such outgrowth was only partially blocked by antiserum to NGF, significant preferential extension of neurites towards stomach persisting in the presence of the antiserum. These results indicate that atrium and stomach produce neuronotrophic factors from the earliest ages studied; the evidence indicates that in the case of atrium, NGF predominates but that stomach produces NGF as well as another factor immunologically distinct from NGF. It is of interest that both types of target explanted before they receive sympathetic innervation show evidence of producing NGF in culture.

Marked increases in calcitonin gene-related peptide-containing nerves in the developing rat following long-term sympathectomy with guanethidine

Changes in the innervation of the cardiovascular system, urinogenital tract and sympathetic and non-sympathetic ganglia have been examined following long-term sympathectomy. Patterns of innervation were investigated using histochemical and immunohistochemical techniques, while levels of noradrenaline and neuropeptides were measured by neurochemical assays. Large doses of guanethidine (50 mg/kg) were given daily for 3 weeks to 8-day-old rat pups, which were killed at 6 or 20 weeks of age. In both age groups noradrenergic nerves were severely depleted or absent, while in some regions dramatic increases of calcitonin gene-related peptide levels were demonstrated. This was revealed by an increase in the density of nerve fibres and in calcitonin gene-related peptide content (up to 18-fold), most notably in the right atrium and superior cervical ganglion. No changes in substance P- or vasoactive intestinal polypeptide-immunolabelled nerves were seen. Conversely, short-term sympathectomy by 6-hydroxy-dopamine treatment caused a depletion of noradrenaline which was not accompanied by an increase in the number or content of calcitonin gene-related peptide-immunolabelled nerves. The possibility that nerve growth factor is involved in the mechanism of hyperinnervation by calcitonin gene-related peptide-containing sensory nerves following long-term sympathectomy is discussed.

Reduction in sympathetic neuronotrophic activity in the pulp of the cat canine tooth after denervation

Most of the nerve fibres supplying the mandibular canine on one side were interrupted by sectioning the inferior alveolar nerve (IAN) and, after 1 week, the trophic activity in each mandibular canine pulp was assessed in an in vitro assay using sympathetic neurones from 11-day chick embryos as test cells. In eight of nine animals tested, neuronotrophic activity in the denervated pulp was markedly lower than in the contralateral control pulp. Antiserum to mouse nerve growth factor had no effect on the trophic activity in either control or denervated pulps. Thus, the pulp differs from other peripheral tissues, which undergo increases in neuronotrophic activity after denervation. The basis of this difference may be the high innervation density of the pulp. The IAN distal to the site of nerve transection also had reduced survival-promoting activity.

Electrophysiological study of conditioning lesion effects on rat sciatic nerve regeneration following either prior section or freeze. II. Blocking by prior tenotomy

The conditioning lesion effects refer to the earlier formation and the accelerated regeneration of axonal sprouts following two successive axotomies. In a previous study, we observed that a prior freeze or a prior cut of rat sciatic nerve resulted in differences in the enhancement of the regeneration rate and the reduction of the initial delay. These differences were interpreted as a possible non-neuronal cells influence on the intrinsic regulation of the conditioning lesion phenomenon. In the present study, we attempted to modify the status of the muscles using tenotomy before the prior nerve injury to determine the respective influence of the muscular cells on conditioning lesion effects. Thus, the conditioning lesion, which was either a cut or a freeze of the tibial nerve at the ankle, was performed 14 days after foot sole muscles were tenotomized, close to their insertion into the calcaneus bone. The test lesion was always a freeze of the sciatic nerve at midthigh performed 7 days following the prior lesion. The elongation of the regenerating sprouts was electrophysiologically evaluated and the regeneration rate as well as the initial delay were calculated by means of regression analysis. Tenotomy did not influence the regeneration as was demonstrated in a group with a single sciatic nerve lesion. In contrast, when prior lesion was performed, the tenotomy prevented both the enhancement of the rate of regeneration and the reduction of the initial delay, whatever was the type of the conditioning lesion.(ABSTRACT TRUNCATED AT 250 WORDS)

Endogenous chicken nerve growth factor from sheath cells is transported in regenerating nerve

We report the presence of endogenous nerve growth factor (NGF) in chicken peripheral nerve. The molecule has been detected with antibodies to mouse salivary gland NGF, using immunohistochemical and immunoelectrophoretic techniques. Previous studies have shown that these antibodies inhibit the survival activity of extracts of chicken peripheral nerve. The NGF accumulated distal, but not proximal, to a ligature placed on a peripheral sympathetic nerve demonstrating that it was retrogradely transported. This transport was detected in intact nerve fibers as well as in nerves from which the peripheral target had been ablated 6 hr or 7 days previously. The results indicate that avian NGF is present in adult chicken peripheral nerves and that this molecule shares antigenic determinants with the mouse molecule. The results further demonstrate that regenerating neurons retrogradely transport NGF supplied by cells within the peripheral nerve (presumably Schwann). The possibility that these cells also provide NGF to intact neurons is discussed.

Sympathetic neuronotrophic activity in the pulp of the cat canine tooth

Extracts of these dental pulps from adult cats contained a non-dialysable agent or agents which could support neurone survival and neurite development for at least three days in neurone-enriched cultures of sympathetic ganglion cells from 11-day chick embryos. The neurone survival-promoting activity differed from nerve growth factor (NGF) in that: (1) anti-mouse NGF serum did not inhibit it; (2) nearly all ganglionic neurones survived in optimum concentrations of pulp extract, whereas only about 35 per cent were supported by NGF; and (3) cell bodies of NGF-supported neurones were markedly larger than in neurones supported by pulp extracts. The neuronotrophic activity in individual dental pulps was highly variable among different cats, but similar between mandibular canines from the same animal. Smaller pulps had higher concentrations of trophic activity than larger ones. Gingival tissue and the anterior belly of the disgastric muscle contained little neuronotrophic activity.

Increase in neuronotrophic activity during the period of smooth muscle innervation

The expansor secundariorum is a unique smooth muscle of the avian wing that receives a dense sympathetic innervation and contains high concentrations of survival factors for sympathetic neurons. In the present study it has been possible to simultaneously examine the appearance of the neuronotrophic activity and the arrival of nerve fibres during the period of innervation. The results show that catecholamine containing nerve fibres can first be detected within the muscle on the fourteenth day of incubation (stage 40) followed by a rapid increase in the density of fibres during the next few days until the adult pattern is reached shortly before hatch. Biochemical estimation of the innervation process by measurement of dopamine beta-hydroxylase activity was supported by the histochemical findings. Estimation of neuronotrophic activity revealed that muscle from stage 40 embryos contains only low levels of activity which increases rapidly as innervation proceeds and further, that this increase in neuronotrophic activity was directly correlated with the dopamine beta-hydroxylase activities. Possible mechanisms regulating this dramatic increase in the specific activity of trophic factors are discussed.