Effect of guanethidine on dopamine in small intensely fluorescent cells of the superior cervical ganglion of the rat

The superior cervical ganglia modulate ventilatory responses to hypoxia independently of preganglionic drive from the cervical sympathetic chain

Superior cervical ganglia (SCG) postganglionic neurons receive preganglionic drive via the cervical sympathetic chains (CSC). The SCG projects to structures like the carotid bodies (e.g., vasculature, chemosensitive glomus cells), upper airway (e.g., tongue, nasopharynx), and to the parenchyma and cerebral arteries throughout the brain. We previously reported that a hypoxic gas challenge elicited an array of ventilatory responses in sham-operated (SHAM) freely moving adult male C57BL6 mice and that responses were altered in mice with bilateral transection of the cervical sympathetic chain (CSCX). Since the CSC provides preganglionic innervation to the SCG, we presumed that mice with superior cervical ganglionectomy (SCGX) would respond similarly to hypoxic gas challenge as CSCX mice. However, while SCGX mice had altered responses during hypoxic gas challenge that occurred in CSCX mice (e.g., more rapid occurrence of changes in frequency of breathing and minute ventilation), SCGX mice displayed numerous responses to hypoxic gas challenge that CSCX mice did not, including reduced total increases in frequency of breathing, minute ventilation, inspiratory and expiratory drives, peak inspiratory and expiratory flows, and appearance of noneupneic breaths. In conclusion, hypoxic gas challenge may directly activate subpopulations of SCG cells, including subpopulations of postganglionic neurons and small intensely fluorescent (SIF) cells, independently of CSC drive, and that SCG drive to these structures dampens the initial occurrence of the hypoxic ventilatory response, while promoting the overall magnitude of the response. The multiple effects of SCGX may be due to loss of innervation to peripheral and central structures with differential roles in breathing control.NEW & NOTEWORTHY We present data showing that the ventilatory responses elicited by a hypoxic gas challenge in male C57BL6 mice with bilateral superior cervical ganglionectomy are not equivalent to those reported for mice with bilateral transection of the cervical sympathetic chain. These data suggest that hypoxic gas challenge may directly activate subpopulations of superior cervical ganglia (SCG) cells, including small intensely fluorescent (SIF) cells and/or principal SCG neurons, independently of preganglionic cervical sympathetic chain drive.

Epidermal adrenergic signaling contributes to inflammation and pain sensitization in a rat model of complex regional pain syndrome

In many patients, the sympathetic nervous system supports pain and other features of complex regional pain syndrome (CRPS). Accumulating evidence suggests that interleukin (IL)-6 also plays a role in CRPS, and that catecholamines stimulate production of IL-6 in several tissues. We hypothesized that norepinephrine acting through specific adrenergic receptors expressed on keratinocytes stimulates the production of IL-6 and leads to nociceptive sensitization in a rat tibial fracture/cast model of CRPS. Our approach involved catecholamine depletion using 6-hydroxydopamine or, alternatively, guanethidine, to explore sympathetic contributions. Both agents substantially reduced nociceptive sensitization and selectively reduced the production of IL-6 in skin. Antagonism of IL-6 signaling using TB-2-081 also reduced sensitization in this model. Experiments using a rat keratinocyte cell line demonstrated relatively high levels of β2-adrenergic receptor (β2-AR) expression. Stimulation of this receptor greatly enhanced IL-6 expression when compared to the expression of IL-1β, tumor necrosis factor (TNF)-α, or nerve growth factor. Stimulation of the cells also promoted phosphorylation of the mitogen-activated protein kinases P38, extracellular signal-regulated kinase, and c-Jun amino-terminal kinase. Based on these in vitro results, we returned to animal testing and observed that the selective β2-AR antagonist butoxamine reduced nociceptive sensitization in the CRPS model, and that local injection of the selective β2-AR agonist terbutaline resulted in mechanical allodynia and the production of IL-6 in the cells of the skin. No increases in IL-1β, TNF-α, or nerve growth factor levels were seen, however. These data suggest that in CRPS, norepinephrine released from sympathetic nerve terminals stimulates β2-ARs expressed on epidermal keratinocytes, resulting in local IL-6 production, and ultimately, pain sensitization.

Depletion and recovery of catecholamines in several organs of rats treated with reserpine

Chemical sympathectomy with reserpine depletes catecholamines in every neuronal or nonneuronal cell producing a nonspecific temporal sympathectomy. After reserpine administration, most of the drug is distributed to tissues based on their blood flow and would then either be metabolized or be reversibly bound in lipid depots from where it might be released. Consequently, reserpine concentration and the catecholamine-depleting effect in the various tissues are expected to differ according to the route of administration. This study was designed to compare the effects of intraperitoneal (i.p.) and subcutaneous (s.c.) administration of reserpine on catecholamine depletion and recovery in the liver, portal vein, and adrenal gland on days 1, 4, and 10 after reserpine dosage. Catecholamine determinations were extended to 25 days after the treatment only in s.c. reserpine-treated rats and adding samples of heart and brown adipose tissue to the testing. I.p. and s.c. reserpine administration had the same norepinephrine-depleting effect in the portal vein and liver but full recovery was present in both tissues only in i.p. reserpine-treated rats. In the adrenal gland, both routes of administration produced the same depleting and recovery effect of norepinephrine and epinephrine concentrations. A significant temporary overshoot in epinephrine levels was observed several days after s.c. reserpine treatment. Except for the liver, reserpine injected s.c. depleted norepinephrine concentrations significantly in all other tissues up to the end of the experiment. Our results suggest that chemical sympathectomy caused by reserpine administered s.c. produces a generalized and prolonged decrease in peripheral sympathetic activity that could be compensated by an increase in activity of the adrenal gland.

Epinephrine and dopamine colocalization with norepinephrine in various peripheral tissues: guanethidine effects

Chemical sympathectomy with guanethidine (Gnt) selectively destroys the postganglionic noradrenergic neurons, whereas dopaminergic fibers and nonneural catecholamine-secreting cells are spared. As a result, the relative proportions of norepinephrine (NE), epinephrine (E), and dopamine (DA) in tissues can be differentially affected. This study was done to show the possible differences in the relative amount of catecholamines in some organs and tissues that might indicate the nature of the secretory cells from which they originate. The contents of NE, E, and DA were assessed in rats neonatally treated with Gnt. Gnt-treated rats showed significantly lower levels of NE (P < 0.01) in all tissues except the adrenal gland and paraganglia. Epinephrine was present in all tissues with mean levels below 25 ng/g, with the exception of the adrenal gland (700 microg/gland) and paraganglia (100 ng/g). Only the heart showed lower values in Gnt-treated rats. Mean DA levels were also very high in paraganglia (530 ng/g). In the Gnt-treated rats, DA levels fell practically to zero except in the duodenum, mesentery, and adrenal, whereas there were high levels in the paraganglia, which were significantly different from controls. The results suggest that the three catecholamines are contained mainly in noradrenergic sympathetic fibers of muscle, white adipose tissue, heart, liver, pancreas, and spleen. The duodenum and mesentery may have dopaminergic fibers or E- and DA-containing nonneural cells. Hepatic-vagus paraganglia contain all the catecholamines in relatively high amounts in nonneural cells, and Gnt treatment raises DA levels without affecting the other amines.

Chemical sympathectomy alters food intake and thermogenic responses to catecholamines in rats

It has been suggested that the sympathetic nervous system contributes to the short-term control of feeding. The adrenergic innervation of some splanchnic organs seems to be especially involved in such processes, since catecholamines reduce feeding only when injected intraperitoneally or intraportally. In this work, the effects of neonatal sympathetic denervation with guanethidine (Gnt) upon food intake were assessed in adult rats. Gnt-treated male rats had lower body weight gain. The hypophagic response to intraperitoneal (ip) norepinephrine was 70% higher in Gnt-treated animals as compared to controls (P < 0.05); that of epinephrine (E) by 33% (P < 0.05) and that of isoproterenol was not significantly modified. As in normal rats, the hypophagic effect was much stronger after ip than after intramuscular (im) administration (P < 0.05). On the other hand, resting oxygen consumption (VO2) was consistently lower in denervated animals. Ip E administration did not modify VO2, while im E caused increased motor activity and VO2 (P < 0.05). In contrast to control rats, the respiratory exchange ratio in ad libitum fed Gnt rats did not decrease after Ip E administration, suggesting a lack of effect upon lipid mobilization. The lower rate of body weight gain induced by neonatal Gnt sympathectomy might be due to lower daily food intake possibly related, in part, to the sensitization of the alpha-adrenergic porto-hepatic response to endogenous catecholamines. Compared with controls, Gnt-treated rats also showed a limited thermogenic capacity not related to feeding, and a greater degree of carbohydrate oxidation, possibly due to a defect in E-induced lipolysis, which is beta-adrenergic.

Plasticity in the phenotypic expression of catecholamines and vasoactive intestinal peptide in adult rat superior cervical and stellate ganglia after long-term hypoxia in vivo

Sympathetic ganglia in the adult rat contain various populations of nerve cells which demonstrate plasticity with respect to their transmitter phenotype. The plasticity of the neuronal cell bodies and of the small intensely fluorescent cells in the superior cervical and stellate ganglia in response to hypoxia in vivo (10% O2 for seven days) was assessed by studying the expression of catecholamines and vasoactive intestinal peptide. The levels of norepinephrine, dopamine, 3,4-dihydroxyphenylacetic acid and vasoactive intestinal peptide immunoreactivity were determined. In addition, the density of the immunohistochemical staining of cells for tyrosine hydroxylase and vasoactive intestinal peptide was evaluated. In the intact superior cervical ganglion, hypoxia increased the dopamine level as well as the density of small intensely fluorescent cells immunolabelled for tyrosine hydroxylase and vasoactive intestinal peptide. In the axotomized ganglion, hypoxia elicited a twofold rise in the level of the vasoactive intestinal peptide as well as enhancing the density of neuronal cell bodies immunostained for this peptide. Thus, the effect of hypoxia on the expression of vasoactive intestinal peptide expression in neurons was dependent on neural interactions. In the intact stellate ganglion, hypoxia alone induced a 1.5-fold increase in the density of neuronal cell bodies immunostained for vasoactive intestinal peptide. Thus, ganglia-specific factors appeared to play a role in determining changes in neuronal phenotype in response to hypoxia. The present study provides evidence for the involvement of dopamine and vasoactive intestinal peptide in ganglionic responses to long-term hypoxia as well as for differential responses by the two ganglionic cell populations, i.e. neuronal cell bodies and small intensely fluorescent cells. Changes in the expression of the vasoactive intestinal peptide during long-term hypoxia may be of energetic, trophic and/or synaptic significance. Hypoxia may be considered to be a vasoactive intestinal peptide-inducing factor in sympathetic ganglia.

Small intensely fluorescent cells of the rat paracervical ganglion synthesize adrenaline, receive afferent innervation from postganglionic cholinergic neurones, and contain muscarinic receptors

In the paracervical ganglion (PCG) of the rat, double-labelling immunofluorescence for catecholamine-synthesizing enzymes and HPLC measurement of catecholamine contents were first performed to evaluate whether intraganglionic small intensely fluorescent (SIF) cells are capable of synthesizing adrenaline. Immunolabelling for tyrosine hydroxylase (TH), dopamine beta-hydroxylase and phenylethanolamine-N-methyl transferase (PNMT) occurred in all SIF cells of the PCG, thus demonstrating the presence of all the enzymes required for adrenaline biosynthesis. Adrenaline levels were undetectable in the PCG but to test the hypothesis that PNMT is active in SIF cells, catecholamines were measured in ganglia of rats pretreated with pargyline, an inhibitor of the monoamine oxidase, the major enzyme involved in the catecholamine degradation. Pargyline treatment increased adrenaline levels in the PCG, thus demonstrating that SIF cells are capable of adrenaline synthesis. The undetectable levels of adrenaline in the PCG of untreated rats suggested a slow rate of biosynthesis of adrenaline in the ganglion. Furthermore, the use of double-labelling showed that SIF cells of the PCG were stained for muscarinic receptors and were approached by varicose ChAT-immunoreactive nerve fibres. Nerve fibres immunoreactive for ChAT were also observed associated with nerve cell bodies of ganglion neurones. Following deafferentation of the PCG, the ChAT-immunoreactive nerve fibres surrounding nerve cell bodies totally disappeared indicating their preganglionic origin, while those associated with SIF cells did not degenerate, which demonstrate that they derived from intraganglionic cholinergic neurones. Taken together, the results show that adrenaline may be a transmitter for SIF cells in the PCG and suggest that cholinergic neurones of the parasympathetic division of the PCG can modulate the SIF cell activity through the activation of muscarinic receptors.

Administration of interleukin-1 at birth affects dopaminergic neurons in adult mice

Interleukin-1 beta (IL-1 beta), a cytokine that plays a relevant role during inflammatory and immune processes, can also affect brain neurotransmitters and the activity of peripheral sympathetic nerves. Because both brain and peripheral catecholaminergic systems in mice are not fully developed at birth, we speculated that the development of these systems may be susceptible to modifications when mice are exposed to IL-1 beta early in life. Here we report that the administration to mice of a low dose of IL-1 beta during the first days of life results in a decreased dopamine content in the hypothalamus in adulthood. We also show that the dopamine content of the superior cervical sympathetic ganglia was reduced in adult mice that were treated with IL-1 beta at birth. No changes in noradrenaline content nor in its metabolite MHPG were detected in the brain and peripheral sympathetic ganglia of these animals. This indicates that central and probably also peripheral dopaminergic neurons are preferentially affected by IL-1 beta treatment at birth. Collectively, these results indicate that an increased production of IL-1 beta during infectious or inflammatory processes in the perinatal period may induce long-lasting, probably permanent, alterations in central and peripheral neurotransmitter systems.

Peripheral chemosensitivity and central integration: neuroplasticity of catecholaminergic cells under hypoxia

The plasticity of catecholaminergic cells within the carotid body, brainstem and sympatho-adrenal system was analyzed in rats subjected to normobaric hypoxia (10% O2) lasting up to 3 weeks. Long-term hypoxia elicited structural, neurochemical and phenotypic changes in carotid body and sympathetic ganglia (SIF cells), and stimulated the norepinephrine turnover in A2 neurons located caudal to the obex, the area where the chemosensory nerve fibers end. Chemodenervation abolished central alterations. Adaptive mechanisms for increasing norepinephrine biosynthesis in hypoxia involved changes in activity of pre-existing tyrosine hydroxylase, the rate-limiting enzyme of catecholamine biosynthesis, and induction of new tyrosine hydroxylase protein. These neurochemical changes occurred after sustained hypoxia only, suggesting that noradrenergic neurons are involved in the central chemoreceptor pathway during sustained hypoxia but are not essential for regulatory responses to acute hypoxia. Acute hypoxia elicited the expression of c-Fos protein in neurons located in nucleus tractus solitarius that were not catecholaminergic. Noradrenaline released under long-term hypoxia could play a neuromodulatory role in ventilatory acclimatization. Cardiovascular responses to hypoxia are mediated by changes in sympatho-adrenal outflow, different according to the target organ. Cardiac sympathetic output and adrenal secretion were stimulated independently of carotid body chemoafferents. Early postnatal hypoxia induced long-term neurochemical changes in carotid body, brainstem and sympathetic efferents that may reveal alterations in development of neurons involved in the chemoreceptor pathway.

Long-term impairment in the neurochemical activity of the sympathoadrenal system after neonatal hypoxia in the rat

The study evaluates the long-term effect of neonatal hypoxia on the neurochemical activity of the sympathoadrenal system in the rat. One-day-old male pups were exposed to hypoxia (10% O2) for 6 d and thereafter reared under normoxia. Neonatal hypoxia reduced the body weight of 3- and 8-wk-old rats and did not change the blood pressure at 6 wk of age. In sympathetic ganglia, the content and/or turnover rates of norepinephrine were reduced in neonatal-hypoxic rats of 3 and 8 wk of age, but the content and turnover rates of dopamine were unaltered. The effect was not dependent on the type of ganglion. In the superior cervical ganglion, neonatal hypoxia had a selective effect on the type of catecholamine (dopamine versus norepinephrine), thus suggesting a selective-altered maturation of noradrenergic neurons, but presumably not of the dopaminergic small, intensely fluorescent cells. A long-term deficiency in adrenal activity was the consequence of neonatal hypoxia, as shown by the decrease in the content and turnover rate of dopamine. Neonatal hypoxia elicited a long-term decrease in the content and turnover rates of norepinephrine in heart and lungs but failed to induce a significant effect in kidneys. However, this effect was not tissue-specific. Data provide evidence that a hypoxic episode occurring during a critical period of development in the rat induces a long lasting decrease in the neurochemical activity of the sympathoadrenal system. These results are discussed in terms of their implications for human pathology.

Chemosensitivity, plasticity, and functional heterogeneity of paraganglionic cells in the rat coeliac-superior mesenteric complex

Chemosensitivity and plasticity of paraganglionic cells in the rat coeliac-superior mesenteric complex (CSMC) were investigated at a basal state of normoxia (21% O2) and after long-term moderate hypoxia (10% O2, 14 days). Chemical sympathectomy previous to hypoxia was performed to destroy principal ganglionic neurons and thus to allow measurement of the norepinephrine and dopamine content of paraganglionic cells. At the basal state, the CSMC contained dopaminergic (TH+/DBH-) and noradrenergic (TH+/DBH+) paraganglionic cells, the majority being of the noradrenergic type. After 14 days of hypoxia, this ratio was reversed and dopaminergic cells predominated, as indicated by a twofold increase of TH+ cells and a twofold decrease of DBH+ cells. Biochemically, hypoxia produced an increase in the content (1.6-fold) and utilization (1.4-fold) of dopamine as well as a smaller increase in the content of norepinephrine, with no change in its utilization rate. The dopaminergic activation induced by hypoxia persisted after sympathectomy with guanethidine. It is concluded that paraganglionic cells in the CSMC display a chemosensitive function. Furthermore, our findings indicate that paraganglionic cells are differentially affected by hypoxia, depending on their distribution and the nature of their neuromodulators. The alterations induced by hypoxia point out the phenotypic plasticity developed by paraganglionic cells in adaptation to hypoxia and further demonstrate the functional heterogeneity of this autonomic cell population in the rat CSMC.

Neuronal metabolism of catecholamines: plasma DHPG, DOMA and DOPAC

Pre-synaptic endings of the sympathetic nervous fibers control the metabolism of catecholamines, particularly inactivating norepinephrine after its neuronal recapture. The present study was carried out to investigate this segment of the metabolism of catecholamines through measurements of DHPG, DOMA and DOPAC concentrations in plasma. A sensitive and specific radio-enzymatic assay was developed of which the major characteristic is to include the plasma sample in the incubation mixture without initial extraction of the deaminated metabolites. In the rat, there was a statistically significant correlation between norepinephrine and DHPG in both anesthetized and conscious conditions and after clonidine or guanethidine induced reduction of sympathetic activity; thus it can be suggested that plasma DHPG is a good index of neuronal metabolism of norepinephrine in this animal. In humans, our data indicate an interesting correlation between norepinephrine and DOMA concentrations in plasma in resting conditions and within three hours after clonidine. Further studies need to be carried out to establish whether DOMA is a better index of neuronal metabolism of norepinephrine than DHPG.

Differential effect of guanethidine on dopamine and norepinephrine in rat peripheral tissues

The changes of dopamine (DA) and norepinephrine (NE) were investigated in rat peripheral tissues after guanethidine treatment (50 mg/kg i.p. five days each week) during one week (group 1, n = 10, five injections) and during 2.5 weeks (group 2, n = 8, 13 injections). Guanethidine greatly reduced NE levels in all the analyzed tissues but only partially depleted DA in kidney, bladder, stomach, intestine, lung and liver and in sympathetic ganglia. The differential pattern of changes between DA and NE induced by guanethidine suggests that peripheral DA is distributed in several neuronal or non-neuronal pools, whose presence, nature and contribution varies in the different tissues. Both noradrenergic cell bodies and small intensely fluorescent cells (SIF cells) can contribute to the DA in the superior cervical ganglion. Noradrenergic neurons seem to be the main sources of DA in seminal vesicles, vas deferens, heart and spleen. In addition to noradrenergic nerves, extraneuronal sources could account for a meaningful portion of DA in kidney, gastrointestinal tract, lung and liver. The bladder is the peripheral tissue where DA exhibits the highest resistance to the neurotoxin. Accordingly, these tissues may provide meaningful sources of non-precursor DA pools.

Response of noradrenaline and dopamine to hypoxia and sympathectomy: evidence for an independent dopaminergic reactivity

In order to assess the status of dopamine in the periphery, we submitted rats to sympathectomy (with guanethidine), to hypoxia, and to both, and measured the concentration and turnover of noradrenaline and dopamine in peripheral organs. Sympathectomy decreased noradrenaline content by 96-99% in all the organs tested. In contrast, dopamine content, which was decreased by 90% in the heart, was not significantly changed in the bladder or lungs. Based on dopamine decrease after guanethidine, and on dopamine:noradrenaline ratios in organs, we conclude that in the heart the dopamine is contained mostly in noradrenergic terminals. In other organs it appears to be contained in non-noradrenergic structures. These are found in: the bladder, stomach, lungs, and kidneys, in decreasing importance. We estimated the turnover of noradrenaline by measuring the decrease of its concentration after inhibition of tyrosine hydroxylase with alpha-methyl-p-tyrosine. Among the five organs studied, the turnover of noradrenaline was increased by long-term hypoxia (10% O2, 15 days) in the heart only (+140%). An increase of sympathetic activity during hypoxia was also found in the kidneys and lungs as shown by the increase in turnover of dopamine that was suppressed by sympathectomy. Hypoxia induced large increases in dopamine concentration in the stomach and the lungs (70 and 190% respectively). These increases were not abolished by sympathectomy and we propose that they are related to a chemosensory function of dopamine-containing paraganglia in the stomach and the lung.