Influence of age and splanchnic nerve on the action of melatonin in the adrenomedullary catecholamine content and blood glucose level in the avian group

Summary A single intraperitoneal (IP) melatonin injection (0.5 mg/100 g body wt.) caused an increase in norepinephrine (NE) fluorescence and elevation of NE content in newly-hatched pigeons (Columba livia), but a reduction of NE fluorescence and depletion of NE content in the adrenal medulla of newly-hatched crows (Corvus splendens) after 0.5 h of treatment. In contrast, in adults melatonin caused increase in NE fluorescence and elevation of NE content only in the parakeet (Psittacula krameri).Half an hour of IP melatonin treatment (0.5 mg/100 g body wt.) induced release of epinephrine (E) from the adrenal medulla of newly-hatched pigeon and parakeet. In contrast, in the adults melatonin caused more than a two-fold increase in E in the pigeon, and a significant increase in the crow.Single IP melatonin injection (0.5 mg/100 g body wt.) caused hypoglycemia in the newly-hatched parakeet and adult pigeon, and hyperglycemia in newly-hatched pigeon after 0.5 h of treatment. Melatonin failed to regulate glucose homoeostasis in newly-hatched and adult crow.Splanchnic denervation of the left adrenal gland was performed in the adult pigeon. The right adrenal served as the innervated gland. Melatonin-induced modulation of catecholamines following a single IP injection (0.5 mg/100 g body wt.) revealed significant increases in NE fluorescence and NE content at 4 and 12 h after treatment in the denervated gland only, which gradually approached normal levels 9 days after treatment. In contrast, E content showed more than a two-fold increase over the control value in both the innervated and denervated glands 0.5 and 24 h after treatment. At 9 days after treatment, E content showed significant depletion in the innervated gland.The results of this study indicate that melatonin modulates catechol hormone content in avian adrenal medulla, and also regulates glucose homoeostasis (except in the crow). The splanchnic nerve plays a vital role in the synthesis of NE but has no effect on E.     

Influence of age and splanchnic nerve on glucagon-induced changes of adrenomedullary catecholamine content and blood glucose level in the avian group

Summary Glucagon (0.1 mg · 100 g body wt^-1) increased norepinephrine (NE) content in adult pigeon (31%) and parakeet (58%), decreased NE content in the adrenal medulla of newly-hatched pigeon (36%), parakeet (52%), and crow (44%) 0.5 h after treatment. Epinephrine (E) content decreased to 26% and 59% of control values, respectively, in newly-hatched pigeon and parakeet 0.5 h after treatment. Glucagon produced hyperglycemia irrespective of age and species. The results indicate that aging modulates glucagon-induced changes of catecholamine (CA) content. In the innervated (I) adrenal gland of pigeon, glucagon caused a 31% increase of NE content 0.5 h after injection, a 46% decrease of NE content 12 h after injection, and a 192% increase of NE 24 h after injection. In the I gland of pigeons, glucagon also caused a 61% decrease of E content 4 h after injection, and brought about a 100% increase of E 24 h after injection. Glucagon-induced changes of CA content differ significantly between the I and denervated (D) glands. The results indicate that the splanchnic nerve regulates release and/or resynthesis of CA induced by glucagon.Abbreviations ANOVA analysis of variance - CA catecholamine - D denervated - E epinephrine - I innervated - MS mean sum of squares - NE norepinephrine - PNMT phenylethanolamine-N-methyl transferase - SS sum of squares - SV source of variation - TH tyrosine hydroxylase     

Role of splanchnic nerve on steroid-hormone-induced alteration of adrenomedullary catecholamines in untreated and reserpinized pigeon

Summary The aim of the present investigation was to ascertain (1) the effect of steroid hormones (corticosterone, dexamethasone, deoxycorticosterone, progesterone, testosterone and oestrogen) on the neural regulation of adrenomedullary catecholamine (CA) content, and (2) the neural modulation of the effect of glucocorticoid hormones (corticosterone and dexamethasone) on reserpine-induced resynthesis of CA. The experiment was conducted on unilaterally splanchnic-denervated pigeons. The findings revealed that 7 consecutive days of steroid treatments (2.5 mg·kg b.w.^-1, i.m.) resulted in significant changes of CA content. Interestingly, the changes of epinephrine (E) content differed significantly between the innervated and denervated glands. This clearly indicates that the splanchnic nerve regulates steroid-induced alterations of E content in the pigeon. The results further revealed that the glucocorticoid hormones augmented reserpine-induced resynthesis of CA specifically in the innervated glands. This confirms that the splanchnic nerve is essential for the synergistic action of glucocorticoids and reserpine in accelerating resynthesis of CA.Abbreviations ANOVA analysis of variance - b.w. body weight - CA catecholamine - DBH dopamine--hydroxylase - df degrees of freedom - E epinephrine - i.m. intramuscular - i.p. intraperitoneal - mRNA messenger ribonucleic acid - NE norepinephrine - PNMT phenylethanolamine-N-methyl transferase - TH tyrosine hydroxylase     

Activation of Tyrosine Hydroxylase by Nicotine in Rat Adrenal Gland

The administration of nicotine activates tyrosine hydroxylase in the rat adrenal gland. This activation is apparently maximal 25 min after a single subcutaneous injection of nicotine at 2.3 mg/kg. Repeated injections of nicotine (seven injections once every 30 min) are associated with a persistent activation of adrenal tyrosine hydroxylase for at least 3 h. The nicotinic receptor antagonist hexamethonium does not significantly inhibit the nicotine-mediated activation of tyrosine hydroxylase in innervated adrenal glands. However, hexamethonium completely blocks the activation of adrenal tyrosine hydroxylase by nicotine in denervated adrenal glands. Furthermore, even though a single injection of nicotine activates tyrosine hydroxylase in both innervated and denervated adrenal glands, repeated injections of nicotine do not activate tyrosine hydroxylase in denervated adrenal glands. Our results suggest that the systemic administration of nicotine activates adrenal tyrosine hydroxylase by two mechanisms: (1) via direct interaction with adrenal chromaffin cell nicotinic receptors; and (2) via stimulation of the CNS leading to the release from the splanchnic nerve of substances that interact with adrenal chromaffin cell receptors other than the nicotinic receptor.     

Secretory and structural changes in the parotid salivary gland of sheep and lambs after parasympathetic denervation.

The effect of the parasympathetic nerve supply on the development of the parotid gland in the immature lamb and its maintenance in the adult sheep has been investigated by unilateral postganglionic denervation. Seventy-seven to ninety-three days after denervation secretory activity of the gland was examined and material taken for histological examination. The adult denervated glands secreted at lower rates than the innervated and their atropine-resistant secretory flow was reduced to as low as one fifth of that of the innervated glands. In two lambs an atropine-resistant flow did not develop in the denervated glands: in another two, flows of saliva from the denervated glands were present but were much less than in the contralateral innervated glands. After denervation glands were, with one exception, smaller than the contralateral innervated glands. The acinar cells of the denervated adult and lamb glands were smaller than the cells of the innervated glands but similar in size to those of 7-14 day old unoperated control lambs. Acinar cells in denervated glands had periodic acid Schiff staining material but the staining reaction to pyronin-methyl green was similar in the innervated and denervated. The results indicate that the integrity of the parasympathetic innervation is essential for the development of the parotid gland of the sheep and for its maintenance in the adult animal.     

Darkness-induced changes in noradrenergic input determine the 24 hour variation in beta-adrenergic receptor density in the rat pineal gland: in vivo physiological and pharmacological evidence

In male rats housed under a 14:10 LD cycle (lights on at 0600 h), pineal beta-adrenergic receptors, assessed as 125Iodopindolol (IPIN) binding to membrane preparations, showed a 24 hour variation characterized by a nocturnal increase that peaked around middark (2300 h-0200 h) and a decrease during the latter half of the dark period. Animals exposed to light for 3 hours into the normal dark period showed a similar increase in IPIN binding that was prevented by a single sc injection (0.5 mg/kg) of isoproterenol (ISO). The decrease in IPIN binding observed after middark was prevented both by moving the animals to light at 0200 h and by propranolol administration (20 mg/kg). Likewise, the reduction in IPIN binding was induced in light exposed animals both by ISO administration (in a dose dependent manner) and by injection of norepinephrine (NE) plus the catecholamine uptake blocker desmethylimipramine (DMI). DMI alone was without effect. Chronic denervation of the pineal gland by superior cervical ganglionectomy (SCGx) increased IPIN binding to levels not higher than those observed at middark. The results suggest that rat pineal beta-adrenergic receptors are regulated in a rhythmic 24 hour pattern. A decrease in density (downregulation) induced by a darkness-associated increase in NE release, occurs late in the night before lights on; recovery from the down regulated state (upregulation) occurs during the light and early dark phase, reaching a maximum density of beta-adrenergic receptors at middark not different from that observed in chronically denervated pineal glands.     

Effect of melatonin on norepinephrine,epinephrine, and corticosterone contents in the adrenal gland of three avian species

Summary A single melatonin injection was administered intraperitoneally to three avian species in two doses (250 and 500 g · 100 g body wt^–1). Norepinephrine (NE), epinephrine (E), and corticosterone (C) contents of the adrenal gland were measured spectrofluorometrically 0.5, 2, and 24 h after injection. The results showed that melatonin at the lower dose caused a decrease of NE content in bulbul (42%), babbler (52%), and pigeon (39%), while at the higher dose it resulted in a decrease of NE only in bulbul (51%) 0.5 h after treatment. Melatonin at the lower dose also caused a decrease of NE in bulbul (45%) and babbler (53%) 2 and 24 h, respectively, after treatment, while at the higher dose it resulted in an increase of NE in bulbul (82%) and a decrease of NE in babbler (44%) 24 h after injection.Both low and high doses of melatonin resulted in a decrease of E content in bulbul (32–43%), babbler (34–43%), and pigeon (44–56%) 0.5 h after treatment, and a 34–46% decrease of E in bulbul and a 32–33% decrease of E in babbler 2 h after treatment. A 57% decrease of E was evident in pigeon with the lower dose of melatonin 2 h after injection. Melatonin at the higher dose caused a 67% increase of E in babbler and a 41% decrease of E in pigeon 24 h after administration. Melatonin at the lower dose resulted in an increase of C content in bulbul (70%), babbler (132%), and pigeon (69%) 0.5 h after treatment. A 60% increase of C was evident in pigeon following the lower dose of melatonin 24 h after injection. Melatonin at the higher dose resulted in an increase of C in the bulbul of 72% and 86% at 0.5 and 24 h, respectively, after treatment. The results indicate that melatonin produces significant changes of NE, E, and C contents in three avian species. The lower dose appears to be more effective in changing NE and C content.Abbreviations C corticosterone - CA catecholamine - DBH dopamine -hydroxylase - E epinephrine - NE norepinephrine     

Splanchnic sympathetic nerves in the development of mild DOCA-salt hypertension

We previously reported that mild deoxycorticosterone acetate (DOCA)-salt hypertension develops in the absence of generalized sympathoexcitation. However, sympathetic nervous system activity (SNA) is regionally heterogeneous, so we began to investigate the role of sympathetic nerves to specific regions. Our first study on that possibility revealed no contribution of renal nerves to hypertension development. The splanchnic sympathetic nerves are implicated in blood pressure (BP) regulation because splanchnic denervation effectively lowers BP in human hypertension. Here we tested the hypothesis that splanchnic SNA contributes to the development of mild DOCA-salt hypertension. Splanchnic denervation was achieved by celiac ganglionectomy (CGX) in one group of rats while another group underwent sham surgery (SHAM-GX). After DOCA treatment (50 mg/kg) in rats with both kidneys intact, CGX rats exhibited a significantly attenuated increase in BP compared with SHAM-GX rats (15.6 ± 2.2 vs. 25.6 ± 2.2 mmHg, day 28 after DOCA treatment). In other rats, whole body norepinephrine (NE) spillover, measured to determine if CGX attenuated hypertension development by reducing global SNA, was not found to be different between SHAM-GX and CGX rats. In a third group, nonhepatic splanchnic NE spillover was measured as an index of splanchnic SNA, but this was not different between SHAM (non-DOCA-treated) and DOCA rats during hypertension development. In a final group, CGX effectively abolished nonhepatic splanchnic NE spillover. These data suggest that an intact splanchnic innervation is necessary for mild DOCA-salt hypertension development but not increased splanchnic SNA or NE release. Increased splanchnic vascular reactivity to NE during DOCA-salt treatment is one possible explanation.     

Vagal afferent activity and renal nerve release of dopamine

To investigate the involvement of vagal afferents in renal nerve release of catecholamines, we compared norepinephrine, dopamine, and epinephrine excretion from innervated and chronically denervated kidneys in the same rat. The difference between innervated and denervated kidney excretion rates was taken as a measure of neurotransmitter release from renal nerves. During saline expansion, norepinephrine excretion from the innervated kidney was not statistically greater than from denervated kidneys. Vagotomy increased norepinephrine release from renal nerves. Thus vagal afferents participated in the suppression of renal sympathetic nerve activity during saline expansion. No significant vagal control of dopamine release by renal nerves was detected under these conditions. Bilateral carotid ligation stimulated renal nerve release of both norepinephrine and dopamine in saline-expanded rats. The effects of carotid ligation and vagotomy were not additive with respect to norepinephrine release by renal nerves. However, the baroreflex-stimulated renal nerve release of dopamine was abolished by vagotomy. Electrical stimulation of the left cervical vagus with a square wave electrical pulse (0.5 ms duration, 10 V, 2 Hz) increased dopamine excretion exclusively from the innervated kidney of hydropenic rats. No significant change in norepinephrine excretion was observed during vagal stimulation. Increased dopamine excretion during vagal stimulation was associated with a larger natriuretic response from the innervated kidney than from its denervated mate (p less than 0.05). We conclude that under appropriate conditions vagal afferents stimulate renal release of dopamine and produce a neurogenically mediated natriuresis.     

Neuromuscular activity impairs axonal sprouting in partially denervated muscles by inhibiting bridge formation of perisynaptic Schwann cells

Following partial denervation of rat hindlimb muscle, terminal Schwann cells extend processes from denervated endplates to induce and guide sprouting from the remaining intact axons. Increased neuromuscular activity significantly reduces motor unit enlargement and sprouting during the acute phase of sprouting. These findings led to the hypothesis that increased neuromuscular activity perturbs formation of Schwann cell bridges and thereby reduces sprouting. Adult rat tibialis anterior (TA) muscles were extensively denervated by avulsion of L4 spinal root and were immediately subjected to normal caged activity or running exercise (8 h daily) for 3, 7, 14, 21, and 28 days. Combined silver/cholinesterase histochemical staining revealed that the progressive reinnervation of denervated endplates by sprouts over a 1 month period in the extensively partially denervated TA muscles was completely abolished by increased neuromuscular activity. Immunohistochemical staining and triple immunofluorescence revealed that the increased neuromuscular activity did not perturb the production of Schwann cell processes, but prevented bridging between Schwann cell processes at innervated and denervated endplates. Our findings suggest that failure of Schwann cell processes to bridge between endplates accounts, at least in part, for the inhibitory effect of increased neuromuscular activity on sprouting.     

Corelease of neuropeptide Y like immunoreactivity with catecholamines from the adrenal gland during splanchnic nerve stimulation in anesthetized dogs

The release of neuropeptide Y like immunoreactivity (NPY-li) from the adrenal gland was studied in relation to the secretion of catecholamines (CA: NE, norepinephrine; E, epinephrine) during the left splanchnic nerve stimulation in thiopental-chloralose anesthetized dogs (n = 16). Plasma concentrations of NE, E, and NPY-li were determined in the left adrenal venous and aortic blood. Adrenal outputs of NPY-li, NE, and E were 2.4 +/- 0.4, 1.4 +/- 0.2, and 7.3 +/- 1.7 ng/min, under basal conditions, respectively. These values increased significantly (p less than 0.05; n = 8) in response to a continuous stepwise stimulation at frequencies of 1, 3, and 10 Hz given at 3-min intervals during 9 min, reaching a maximum output of 4.6 +/- 0.9 (NPY-li), 240.2 +/- 50.2 (NE), and 1412.5 +/- 309.7 ng/min (E) at a frequency of 10 Hz. Burst electrical stimulation at 40 Hz for 1 s at 10-s intervals for a period of 10 min produced similar increases (p less than 0.05) in the release of NPY-li (4.8 +/- 1.0 ng/min, n = 8), NE (283.5 +/- 144.3 ng/min, n = 8), and E (1133.5 +/- 430.6 ng/min, n = 8). Adrenal NPY-li output was significantly correlated with adrenal NE output (r = 0.606; n = 24; p less than 0.05) and adrenal E output (r = 0.640; n = 24; p less than 0.05) in dogs receiving the burst stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)     

The role of sub-optimal preovulatory oestradiol secretion in the aetiology of premature luteolysis during the short oestrous cycle in the cow

Premature regression of the corpus luteum, following the first post partum ovulation, is often preceded by sub-optimal preovulatory oestradiol secretion and accompanied by elevated levels of oxytocin receptors early in the luteal phase. We have investigated the role of preovulatory oestradiol in the control of subsequent oxytocin receptor concentration and activity by treating ovariectomised cows, over a simulated 48 h follicular phase, with high (600 microg per day) medium (300 microg per day) or low (150 microg per day) levels of oestradiol. These doses of oestradiol generated mean+/-S.E.M. plasma oestradiol concentrations of 12.1+/-1.0, 4.9+/-0.5 and 2.9+/-0.4 pg ml(-1), respectively. In Study 1 (n=4 per group), we found that by day 4 following oestrus there was a significant (P< 0.05) effect of the level of oestradiol on the inhibition of oxytocin binding activity measured in endometrial biopsy samples. This had fallen to mean+/-S.E.M. concentrations of 25+/-2 fmol per mg protein in the high group, 47+/-8 fmol per mg protein in the medium group and 65+/-12 fmol per mg protein in the low group. In Study 2, cows (n=3 per group) were treated with the same three levels of oestradiol followed by treatment with increasing levels of progesterone from days 3 to 6 following oestrus, generating mean+/-S.E.M. plasma concentrations of 2.17+/-0.18 ng ml(-1) by day 6. On day 6, there was a significant (P< 0.01) effect of the level of oestradiol on PGF(2alpha) release in response to oxytocin challenge. High, medium and low oestradiol groups exhibiting mean+/-S.E.M., increase plasma PGF(2alpha) metabolite concentrations of 10.0+/-2.2, 21.3+/-4.3 and 41.3+/-1.2 pg ml(-1), respectively, during the hour after oxytocin administration. From these results, we postulate that at the first post partum ovulation a low level of preovulatory oestradiol can result in the early generation of a luteolytic mechanism during the subsequent luteal phase due to impaired inhibition of oxytocin receptors allowing increased PGF(2alpha) release.     

POSTSYNAPTIC ADRENERGIC-CYCLIC AMP CONTROL OF THE SEROTONIN CONTENT OF CULTURED RAT PINEAL GLANDS

Abstract— This investigation was designed to determine whether the amount of serotonin (5-HT) in cultured pineal glands can be altered by norepinephrine (NE). Treatment with l -NE (10^?5-10^?7m ) for 4-6 h caused a gradual decrease in the concentration of 5-HT to a value that was less than 30% of that in the untreated control gland. This effect was observed using chronically denervated pineal glands. d -Norepinephrine (10^?6-10^?7m ) and dopamine (10^?4m ) were ineffective in lowering 5-HT. The effect of l -NE was completely blocked by a β-adrenergic receptor blocker, propranolol and was only slightly decreased by α-adrenergic receptor blockers. These observations indicate that l -NE acts post-synaptically via a highly specific β-adrenergic mechanism. The effect of l -norepinephrine was mimicked by theophylline and N⁶, 2′0-dibutyryl adenosine 3′,5′-monophosphate, an indication that adenosine 3′,5′-monophosphate is involved in the effect of l -NE on 5-HT. Treatment with cycloheximide, which by itself caused a decrease in pineal 5-HT, also blocked any further decrease caused by treatment with l -NE, an indication that protein synthesis is necessary for maintenance of baseline levels of serotonin and for the effect of l -NE to be observed. The total amount of l -[³H]NE and degradation products of L-[³H]NE in the gland after 6 h of treatment with l -[³H]NE was less than 3 pmol. This amount of l -NE and degradation products of l -NE could not account for the decrease of 100-200 pmol of 5-HT on the basis of a mole for mole replacement of 5-HT by l -NE. These findings are consistent with the hypothesis that non-neuronal pineal 5-HT is physiologically regulated by the release of l -NE from the sympathetic nerve network.     

Effect of environmental stress on release of norepinephrine in posterior nucleus of the hypothalamus in awake rats: role of sinoaortic nerves

Norepinephrine(NE) release in posterior nucleus(PH) of the hypothalamus was examined before and during acute shaker (oscillation) stress in sinoaortic denervated(SAD) and sham-operated(SO) rats. NE in PH extracellular fluid of freely moving rats was collected by microdialysis and measured by sensitive radioenzymatic assay. Three days after SAD or SO operation, mean arterial pressure(MAP) and heart rate(HR) were significantly higher in SAD rats than SO rats. Baseline levels of NE in PH dialysate were also significantly elevated in SAD rats. Although five minutes of shaker stress elicited pressor and tachycardic responses coupled with increased NE release in PH of both groups, the increases in MAP and dialysate NE were larger in SAD than SO rats. These findings indicate that noradrenergic neurons in the PH respond to stress-induced stimuli and receive tonic input from baroreflex pathways.     

Evidence for a systemic role for ovarian oxytocin in luteal regression in sheep

Jugular venous concentrations of oxytocin and progesterone changed in parallel during the oestrous cycle in the ewe, falling at luteal regression and rising with formation of the new corpus luteum. These fluctuations in the circulating concentration of oxytocin were not caused by changes in its metabolic clearance rate. On Days 6-9 of the cycle circulating oxytocin concentrations exhibited a diurnal rhythm, peaking at 09:00 h; this rhythm was absent on Days 11-14. Although there was no evidence for increased production of oxytocin at or preceding luteal regression in samples taken daily, more frequent sampling revealed that two thirds of detected surges of uterine secretion of prostaglandin (PG) F-2 alpha were accompanied by raised levels of oxytocin. This oxytocin was not of pituitary origin. Luteal regression induced with cloprostenol on Day 8 after oestrus caused a decrease in circulating progesterone level followed after 24 h by a fall in oxytocin. Measurements of oxytocin in the ovary and other organs before and after treatment with cloprostenol identified the corpora lutea as a major potential source of oxytocin, and suggested that 98% of luteal oxytocin was available for secretion in response to prostaglandin stimulation. The data are consistent with a role for ovarian secretion of oxytocin in response to uterine release of PGF-2 alpha in the control of luteal regression.     

ACTH stimulation of adrenal epinephrine and norepinephrine release

Epinephrine (E) and norepinephrine (NE) levels were measured simultaneously in the adrenal veins of 6 patients before and after stimulation with 0.25 mg beta 1-24 ACTH. In 1 patient with Cushing's syndrome, E and NE were also measured before and 30 min after dexamethasone. There was a significant increase in NE and E secretion (p less than 0.002) from both adrenal glands after ACTH stimulation. In the patient with Cushing's syndrome, there was also a slight increase in plasma E levels after dexamethasone. It is postulated that ACTH stimulated NE and E secretion by augmenting blood flow through the adrenals and by induction of tyrosine hydroxylase and dopamine beta-hydroxylase, although a direct effect of ACTH on NE and E secretion cannot be excluded. It is also possible that the increase in adrenal catecholamine secretion after ACTH may be due to ACTH augmentation of catecholamine secretion by endogenous opioids such as beta-endorphin.     

The effect of etorphine on nicotine- and muscarine-induced catecholamine secretion from perfused rat adrenal glands

The effect of etorphine on nicotine and muscarine-mediated catecholamine (CA) release from isolated perfused rat adrenal glands was investigated. Nicotine increased CA secretion at the low concentration of 0.5 micrograms while higher concentrations of muscarine (5 micrograms) were required. Moreover, muscarine released primarily epinephrine (EP) from rat adrenal glands while nicotine released norepinephrine (NE) and Ep. Etorphine inhibited NE and EP release evoked by nicotine to the same extent, whereas, muscarine-mediated release of NE and EP was not affected. Mecamylamine and verapamil inhibited nicotine but not muscarine-induced CA secretion. Our results suggest that etorphine preferentially interacts with nicotinic receptors on rat adrenal chromaffin cell membranes.     

A Role for Acetylcholine-Nicotinic Receptor Interactions in the Selective Increase of Rat Skeletal Muscle G4 Acetylcholinesterase Following Short-Term Denervation

The present work addresses the effects of short-term denervation on acetylcholinesterase (AChE; EC 3.1.1.7) isoenzymes in anterior gracilis muscles from adult male Sprague-Dawley rats. It examines possible relationships between AChE isoform changes and other denervation phenomena, and evaluates the importance of acetylcholine (ACh)-nicotinic receptor interactions in selectively modulating the activity of G4 AChE. Results confirm that denervation causes a specific, transient increase in G4 AChE and show that: most of the increment can be explained by the hydrophobic species of this isoenzyme; changes in AChE isoforms markedly precede the onset of spontaneous electromechanical activity (fibrillation), as well as acetylcholine receptor (AChR) proliferation; and the G4 AChE response is eliminated when AChRs are blocked by alpha-bungarotoxin treatment performed before but not after (24 h) denervation. These data point to the absence of direct causal relationships between the G4 AChE increment and fibrillation, AChR proliferation, or changes in the release of this isoform from denervated muscle. In turn, they suggest the participation of AChR activation in triggering the G4 AChE response and emphasize the possible role of ACh-AChR interactions in modulating the production of this isoenzyme in not only denervated but also innervated fast-twitch muscles.     

The host range phenotype displayed by a Sindbis virus glycoprotein variant results from virion aggregation and retention on the surface of mosquito cells

The Sindbis virus variant NE2G216 is a PE2-containing host range mutant that is growth restricted in cultured mosquito cells (C6/36) due to inefficient release of virions from this cell type. The maturation defect of NE2G216 has been linked to the structures of N-linked oligosaccharides synthesized by arthropod cells. Analysis of C6/36 cells infected with NE2G216 by transmission electron microscopy revealed the presence of dense virus aggregates within cytoplasmic vacuoles and virus aggregates adhered to the cell surface. The virus aggregation phenotype of NE2G216 was reproduced in vertebrate cells (Pro-5) by the addition of 1-deoxymannojirimycin, an inhibitor of carbohydrate processing which limits the processing of N-linked oligosaccharides to structures that are structurally similar, albeit not identical, to those synthesized in C6/36 cells. We conclude that defective maturation of NE2G216 in mosquito cells is due to virion aggregation and retention on the cell surface and that this phenotype is directly linked to the carbohydrate-processing properties of these cells.