Recent developments in degeneration of the sympathetic neuron

Brainstem noradrenergic neurons: Identifying a hub at the intersection of cognition, motility, and skeletal muscle regulation

Brainstem noradrenergic neuron clusters form a node integrating efferents projecting to distinct areas such as those regulating cognition and skeletal muscle structure and function, and receive dissimilar afferents through established circuits to coordinate organismal responses to internal and environmental challenges. Genetic lineage tracing shows the remarkable heterogeneity of brainstem noradrenergic neurons, which may explain their varied functions. They project to the locus coeruleus, the primary source of noradrenaline in the brain, which supports learning and cognition. They also project to pre-ganglionic neurons, which lie within the spinal cord and form synapses onto post-ganglionic neurons. The synapse between descending brainstem noradrenergic neurons and pre-ganglionic spinal neurons, and these in turn with post-ganglionic noradrenergic neurons located at the paravertebral sympathetic ganglia, support an anatomical hierarchy that regulates skeletal muscle innervation, neuromuscular transmission, and muscle trophism. Whether any noradrenergic neuron subpopulation is more susceptible to damaged protein deposit and death with ageing and neurodegeneration is a relevant question that answer will help us to detect neurodegeneration at an early stage, establish prognosis, and anticipate disease progression. Loss of muscle mass and strength with ageing, termed sarcopenia, may predict impaired cognition with ageing and neurodegeneration and establish an early time to start interventions aimed at reducing central noradrenergic neurons hyperactivity. Complex multidisciplinary approaches, including genetic tracing, specific circuit labelling, optogenetics and chemogenetics, electrophysiology, and single-cell transcriptomics and proteomics, are required to test this hypothesis pre-clinical.

Current approaches to development of the autonomic nervous system: clues to clinical problems

A number of different approaches to autonomic development utilizing a variety of experimental models and analytical techniques have been outlined. A scheme, which attempts to delineate a series of events involving separate but sometimes overlapping mechanisms, is proposed for the complex process of formation and maintenance of functional autonomic neuroeffector junctions. The relevance of these basic mechanisms of a variety of clinical abnormalities of autonomic function is discussed.

Neuroreceptor mRNA expression in the rat mesenteric artery develops independently of innervation

Studies in autonomic targets have shown that nerves may be required for the development and maintenance of postsynaptic receptor populations. We have examined this relationship in the rat mesenteric artery, assessing mRNA expression levels for a range of neuroreceptors after neonatal sympathectomy, using 6-hydroxydopamine or antisera directed against nerve growth factor, and sensory denervation, using capsaicin. Total RNA was extracted from 28 day old rats and reverse transcription-polymerase chain reaction was performed, using primers specific for the alpha1(A,B,D)- and alpha2(A,B,C)-adrenergic, neurokinin (NKI-NK3), muscarinic (M1-M5) and P2X purinergic (P2x1-7) receptor families. Results showed no decreases in mRNA expression of any of the specific receptor subtypes after either sympathetic or sensory denervation. Small increases in mRNA expression were detected following sensory denervation for some of the receptor subtypes. We conclude that neither sympathetic nor sensory nerves are mandatory for the expression of mRNA of a range of neuroreceptors in the mesenteric vascular bed of the rat.

The changes in the nervous structures under the chemical sympathectomy with guanethidine

The process of sympathectomy of white rats was achieved by injecting guanethidine intraperitoneally every day for 5.5 weeks at doses of 75 mg/kg of animal's weight. This process of sympathectomy was checked according to ganglion cervicothoracicum neurocytes state. The material was taken on days 1, 14, 30, 90 and 180 after cessation of guanethidine injections. It was ascertained that full sympathectomy under prolonged injections of high doses of guanethidine is reached at 5-6 months after the cessation of the injections, though pronounced total degeneration of gnl. stellatum neurocytes is marked on the 14th-30th days after cessation of the guanethidine injections. The following gradient of damaging influence of guanethidine was revealed: sympathetic gnl. cervicothoracicum neurocytes gnl. nodosum afferent neurocytes-neuromuscular synapsis skeletal muscle.

Methods of sympathetic degeneration and alteration

The role of the sympathetic nervous system in health and disease has often been elucidated by inducing changes in, or degeneration of sympathetic neural pathways. Several methods of inducing peripheral lesions have been created from surgical removal, NGF depletion, auto-immune and chemical destruction to novel approaches using immunotoxins and transgenic animals. This review compares these methods in terms of their mechanism and specificity. The advantages and disadvantages of these techniques are discussed.

Post-receptor pathway of the ATP-induced relaxation in smooth muscle of the mouse vas deferens

1. The post-receptor pathway of the ATP relaxant effect in K(+)-precontracted vas deferens smooth muscle (VD) was examined. 2. The relaxation to ATP was not antagonized either by 10 microM methylene blue, a cyclic GMP inhibitor, by 10 microM indomethacin, an inhibitor of prostaglandin synthesis or by 100 microM NG-nitro-L-arginine, an inhibitor of NO production. 3. The Rp-diastereomer of adenosine 3':5'-cyclic monophosphorothioate (Rp-cAMPS) 200 microM, a competitive inhibitor of cyclic AMP significantly diminished the relaxant response to ATP. 4. Isoprenaline 10 microM, a beta-adrenoceptor agonist, produced a sustained relaxation, inhibited by Rp-cAMPS, without a significant change in [Ca2+]i, thereby mimicking the ATP-induced relaxant effect. 5. The level of the phosphorylated myosin light chain in the precontracted VD was significantly lowered by 1000 microM ATP. 6. ATP (1000 microM) and isoprenaline (10 microM) produced the same increase (+ 50%) of [cyclic AMP] when applied to a resting VD. 7. The effect of simultaneous increases of [Ca2+]i and of [cyclic AMP] produced by externally applied ATP are discussed. 8. These results suggest that ATP-induced relaxation in K(+)-precontracted VD is mediated by the activation of adenylyl cyclase.

In vitro denervation of the rat vas deferens through hypothermic storage

1. The rat vas deferens was excised, stored at 4-6 degrees C and tested after 24, 48, 72 or 96 h for its contractile activity and for the presence of innervation. 2. The maximal contractile capacity of the vas, tested through cumulative concentrations of barium chloride (3 x 10(-2) M) was progressively reduced from about 110 mm to about 63 mm after 72 h, without further decay after 96 h. Spontaneous rhythmic contractions were practically absent. 3. A loss of endogenous pools of catecholamines was indicated by four parameters: (a) a decline of about 80% after 24 h and of more than 95% after 48 h of the contractile effect of the indirect sympathomimetic agonist tyramine; (b) a fall of about 20%, 50% and 85% on the concentration of noradrenaline, respectively after 24, 48 and 72 h; (c) a fall of about 25% and 90% after respectively 24 and 48 h, of the activity of dopamine-beta-hydroxylase (DBH); (d) a decline of noradrenaline-induced histofluorescence on cross sections of the vas. 4. A loss of neuronal uptake capacity was indicated by: (a) a progressive variation of the apparent affinity for adrenaline, expressed as pD2 values, that increased by about 1.5 log units (corresponding to a 30 fold potentiation) after 72 h, and (b) a reduction of the ability of cocaine to potentiate the contractile effects of adrenaline. 5. The pD2 values for barium chloride, 5-hydroxytryptamine (5-HT) and histamine were not significantly changed, while the corresponding value for acetylcholine was slightly but significantly reduced by about 0.8 log units. 6. The maximal heights of concentration-response curves for noradrenaline, acetylcholine, histamine and 5-HT were reduced by 42-66% in relation to controls. However, when this reduction was measured in relation to the corresponding barium effect, by means of the relative responsiveness ratio (p), a small though significant increase was observed for noradrenaline, and a fall for the other drugs.7. It is concluded that: (1) the values for the various biochemical and pharmacological parameters decline at different rates, though revealing altogether that denervation is completed by at least 85% after 72 h of hypothermic storage; (2) two of the results, i.e., the lack of spontaneous rhythmic contractions and the lack of increased contractile effects for acetylcholine, 5-HT and histamine, indicate that in these conditions the vas is devoid of the so-called nonspecific signs of denervation.

Growth of sympathetic postganglionic axons after partial chemical destruction with guanethidine

Partial sympathectomy of neonatal rats was produced by treatment with guanethidine. The number of neurons of the superior cervical ganglion decreased to 15% of control values and remained constant throughout the subsequent observation period of 4 months. The volume of the remaining neuronal perikarya increased faster than that of control animals during the observation period, and the density of adrenergic innervation of the iris and the noradrenaline content of the heart were found to partially recover after the initial decrease produced by the guanethidine treatment, reaching 33% and 30% of control values, respectively, after 4 months. The noradrenaline content of the duct of the vas deferens was greatly reduced by guanethidine treatment, but almost recovered after 4 months. The frequency of sympathetic preganglionic impulses was elevated throughout the 4 months observation period, and it is suggested that this increase is responsible for the compensatory changes in cell volume, terminal density and terminal noradrenaline content of the remaining neurons.