Nerve growth factor induces functional nicotinic acetylcholine receptors on rat sensory neurons in culture

Neonatal sensory neurons from rat nodose ganglia express nicotinic acetylcholine receptors when grown in tissue culture without other cell types. The present study investigates the role of nerve growth factor in inducing these receptors. Nerve growth factor has little effect on the growth and survival of nodose neurons in culture, although most neurons were found by quantitative radioautography to have high-affinity nerve growth factor receptors. Nerve growth factor strongly influenced the expression of nicotinic receptors on these neurons: the proportion of acetylcholine-sensitive neurons was approximately 60% in cultures with nerve growth factor compared with 15% in cultures grown without nerve growth factor. The proportion of acetylcholine-sensitive neurons increased over the first week, plateaued by day 12 and remained high for at least three weeks. In contrast, without NGF, the proportion of acetylcholine-sensitive neurons was low throughout the three-week period. The results indicate that nerve growth factor is an important factor in promoting nicotinic receptors on these neurons in culture.

Inactivation of A currents and A channels on rat nodose neurons in culture

Cultured sensory neurons from nodose ganglia were investigated with whole-cell patch-clamp techniques and single-channel recordings to characterize the A current. Membrane depolarization from -40 mV holding potential activated the delayed rectifier current (IK) at potentials positive to -30 mV; this current had a sigmoidal time course and showed little or no inactivation. In most neurons, the A current was completely inactivated at the -40 mV holding potential and required hyperpolarization to remove the inactivation; the A current was isolated by subtracting the IK evoked by depolarizations from -40 mV from the total outward current evoked by depolarizations from -90 mV. The decay of the A current on several neurons had complex kinetics and was fit by the sum of three exponentials whose time constants were 10-40 ms, 100-350 ms, and 1-3 s. At the single-channel level we found that one class of channel underlies the A current. The conductance of A channels varied with the square root of the external K concentration: it was 22 pS when exposed to 5.4 mM K externally, the increased to 40 pS when exposed to 140 mM K externally. A channels activated rapidly upon depolarization and the latency to first opening decreased with depolarization. The open time distributions followed a single exponential and the mean open time increased with depolarization. A channels inactivate in three different modes: some A channels inactivated with little reopening and gave rise to ensemble averages that decayed in 10-40 ms; other A channels opened and closed three to four times before inactivating and gave rise to ensemble averages that decayed in 100-350 ms; still other A channels opened and closed several hundred times and required seconds to inactivate. Channels gating in all three modes contributed to the macroscopic A current from the whole cell, but their relative contribution differed among neurons. In addition, A channels could go directly from the closed, or resting, state to the inactivated state without opening, and the probability for channels inactivating in this way was greater at less depolarized voltages. In addition, a few A channels appeared to go reversibly from a mode where inactivation occurred rapidly to a slow mode of inactivation.

Interrelationship between cortisol and atrial natriuretic factor in the immature ovine fetus

1. In chronically cannulated ovine fetuses (100-130 days of gestation) the infusion of cortisol (86.7 +/- 15 micrograms/h for 4 h) or human atrial natriuretic factor (ANF; 4.4 micrograms for 2 h) resulted in highly significant increases in the excretion of sodium, chloride, potassium and water. 2. Cortisol had no significant effect on fetal plasma ANF concentrations. All values are mean and s.e.m. Plasma immunoreactive ANF was 53 +/- 5 and 67.3 +/- 13 pmol/L in the 4 h saline infused fetuses, and 51.3 +/- 14.3 and 74 +/- 13.3 pmol/L in cortisol-infused fetuses (n = 7). A separate group of fetuses received 2 h infusions of saline or hANF (4.4 micrograms/h), and plasma IR-ANF values were measured (n = 3). The values, at 0, 60, 90 and 120 min were, respectively, 19.7 +/- 3, 17.3 +/- 0.7, 18.7 +/- 3.7 and 20.7 +/- 3.7 pmol/L in the saline infused group, and 25.3 +/- 5.3, 80.7 +/- 32.3, 123.3 +/- 4.3 and 100 +/- 15 pmol/L in the ANF-infused fetuses. 3. Blood cortisol concentrations, in fetuses infused for 4 h with 0.9% NaCl, were 3.1 +/- 0.8 nmol/L (n = 7); in fetuses infused with 0.9% NaCl for 2 h were 3.6 +/- 1 nmol/L (n = 3); in fetuses infused for 4 h with cortisol were 19.9 +/- 1.9 nmol/L (n = 7); and in fetuses infused with hANF for 2 h were 6.0 +/- 3.0 nmol/L (n = 5). 4. There was no effect of fetal hANF infusion on maternal or fetal blood aldosterone concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrophysiology of a chick neuronal nicotinic acetylcholine receptor expressed in Xenopus oocytes after cDNA injection

Brain nicotinic acetylcholine receptors (nAChRs) are made up of protein subunits that differ from those constituting muscle nAChRs. To characterize the physiological properties of one class of avian brain nicotinic receptor, we injected the nuclei of Xenopus oocytes with full-length cDNAs for the ligand binding (alpha 4) and structural (n alpha) subunits. Injected oocytes had large ACh-induced currents in the microampere range that were insensitive to alpha-bungarotoxin, as expected for neuronal nAChRs. We found that these brain nAChRs incorporate at least two alpha 4 subunits and that their functional properties differ from muscle nAChRs in at least two respects: the elementary conductance is considerably smaller (20 pS), and channels in outside out patches stop functioning within a few minutes.

Membrane currents of rat satellite cells attached to intact skeletal muscle fibers

Muscle satellite cells play an important role in the postnatal growth of skeletal muscle and in the regeneration of damaged muscle during adult life. Little is known about the physiological properties of satellite cells in their dormant state as they lie adjacent to the intact muscle fibers, underneath the basement membrane. Our recent experiments, using patch clamp techniques, indicate that no tight electrical coupling is present between satellite cells and the muscle fiber dissociated from rat flexor digitorum brevis. Satellite cells possess sodium channels with low sensitivity to tetrodotoxin and at a much lower density than muscle. In addition, satellite cells are insensitive to acetylcholine (ACh) for at least 24 hr after having been removed from the animal, even when detached from their muscle fiber. However, we could measure ACh-evoked currents from satellite cells 48-72 hr in culture, indicating that ACh sensitivity develops with time.

Rapid and selective effects of thyrotropin on [35S]methionine incorporation into cytoplasmic and nuclear proteins in calf thyroid tissue slices

Previous studies have indicated that thyrotropin may induce general increases in RNA and protein synthesis in calf thyroid tissue slices. In this report, we show that thyrotropin selectively stimulates [35S]methionine incorporation into small numbers of specific cytoplasmic and nuclear proteins. We provide data on the time course of stimulation and on relative molecular masses and isoelectric points of hormone-response proteins. Calf thyroid tissue slices were incubated for 3 h, 6 h or 9 h in the presence or absence of thyrotropin (50 mU/ml); [35S]methionine (50-75 microCi/ml) was added for the final 3 h of incubation. Cytoplasmic and nuclear fractions were then prepared, and analyzed by two-dimensional polyacrylamide gel electrophoresis and fluorography. Thyrotropin increased [35S]methionine incorporation into two cytoplasmic and four nuclear proteins within 3 h; hormonal effects on the labeling of five of these six proteins were transient, and no longer evident after 6-9 h. In contrast, a second group of two cytoplasmic and four nuclear proteins exhibited increased labeling after a delay of 6-9 h. Our results suggest that thyrotropin selectively stimulates the synthesis of specific cytoplasmic and nuclear proteins in calf thyroid tissue slices, and that stimulation involves at least two mechanisms (one rapid, the other delayed).

Factors affecting the expression of acetylcholine receptors on rat sensory neurones in culture

Sensory neurones from nodose ganglia of new-born rats were grown in dissociated tissue culture either with or without satellite cells. When cultured without satellite cells, most neurones developed sensitivity to acetylcholine (ACh); time-course experiments indicated that the neurones acquire their sensitivity during the second to third week in culture. Most neurones co-cultured with satellite cells did not develop ACh sensitivity. Delayed removal of satellite cells 8-12 days after plating resulted in few neurones acquiring ACh sensitivity. Delayed addition of satellite cells to neuronal cultures that were initially grown without satellite cells had no effect on the number of ACh-sensitive neurones. The potential to develop ACh sensitivity in culture without satellite cells decreases with the age of the neurones at the time of culturing; few neurones from 2-week-old animals developed sensitivity to ACh when cultured without satellite cells. These results indicate that there is some influence from satellite cells that prevents nodose neurones from developing ACh sensitivity in culture and suggests that this influence may also operate in vivo.

Single-channel analysis of fast transient potassium currents from rat nodose neurones

Single channels that underlie the fast transient potassium current (IA) were recorded, using patch-clamp techniques, from cultured sensory neurones. The open channel conductance was approximately 22 pS, and was constant over most of the physiological voltage range; single-channel conductance decreased at more depolarized levels. Summing single-channel currents resulted in an average current whose kinetics were similar to the macroscopic IA. The inactivation of these currents, at the potentials we studied, was fitted with a single exponential with a time constant of approximately 30 ms. For the currents evoked by large depolarizing steps (to +40 mV), the mean channel open time equals approximately 30 ms. For currents evoked at less depolarized levels (to 0 mV), the mean open time equals approximately 15 ms, half the inactivation time constant.

Thymic seminoma and myasthenia gravis

Computed tomography detected an enlarged thymus in a 27-year-old man with myasthenia gravis of recent onset. Pathological examination of the thymus revealed lymphoid hyperplasia and a thymic seminoma (or germinoma), which was arising as an intramural nodule in a thymic cyst. This is the first reported association of thymic seminoma, lymphoid hyperplasia, and myasthenia gravis.

Hormonal control of the phosphorylation of histones, HMG proteins and other nuclear proteins

Hormone-dependent phosphorylation and dephosphorylation of nuclear proteins may play an important part in regulating nuclear function and specific gene expression. Some progress has been made in identifying specific nuclear proteins whose phosphorylation is affected by specific hormones; however, relatively little is known about the regulatory mechanisms involved, or about the molecular consequences of increased or decreased phosphorylation. It is suspected--but not yet proved--that cAMP-dependent effects on transcription are mediated at least partly by increases in nuclear cAMP-dependent protein kinase (A-kinase) activity, and consequent increases in the phosphorylation of specific chromatin proteins. In several instances, increased phosphorylation has been found to precede or correlate with cAMP-mediated induction of specific gene products. Several chromatin proteins are susceptible to cAMP-dependent phosphorylation in vivo, including histones H1 and H3, the high mobility group protein HMG 14 (which is preferentially associated with actively transcribed chromatin), and at least three other basic nonhistone proteins. The A-kinase phosphorylation sites of the majority of H1, H3 and HMG 14 molecules in chromatin appear to be inaccessible to A-kinase in vivo; nothing is known about the factors determining their accessibility, which may be tightly regulated and may vary significantly from cell to cell and tissue to tissue. Many hormone-induced changes in nuclear protein phosphorylation may be cAMP-independent. cAMP-independent mechanisms could involve a variety of nuclear enzymes including, for example, cGMP-dependent, Ca2+/calmodulin-dependent, Ca2+/phospholipid-dependent and polyamine-dependent protein kinases. So far, however, there is little solid evidence in support of a role for any specific cAMP-independent protein kinase in mediating hormonally induced increases in the phosphorylation of specific, identified nuclear proteins.

Histone and high mobility group protein phosphorylation in the thyroid: regulation by cyclic nucleotides

A variety of cyclic nucleotide analogs and other agents that affect thyroid cyclic nucleotide metabolism were used to investigate the role of cAMP and cGMP in regulating nuclear protein phosphorylation in calf thyroid slices labeled in vitro with [32P]orthophosphate. Two major groups of acid-soluble proteins were studied. Group I consisted of proteins whose phosphorylation is stimulated by TSH [histones H1 and H3, high mobility group (HMG) protein 14, and the HMG 14/17-like protein PS.3]; group II included representatives of a spectrum of proteins whose phosphorylation is unaffected by TSH (histones H2A, H2B, and H4, HMG 17, the HMG 14/17-like protein PS.2, and the nonhistone protein AS.1). The effects of TSH (50 mU/ml) on the 32P labeling of group I proteins were partially reproduced by (Bu)2cAMP (1 mM), 8-bromo-cAMP (1 mM), and butyrate (2 mM), and closely mimicked by 8-(4-chlorophenylthio)cAMP (1 mM), forskolin (25 microM), and butyrate (10 mM). (Bu)2cGMP (1 mM), 8-bromo-cGMP (1 mM), and carbachol (50 microM) had no effect on protein phosphorylation. NaNO2 (20 mM), which markedly increases cGMP concentration in calf thyroid slices, decreased the 32P labeling of group I proteins and also affected, to varying extents, the phosphorylation of the group II proteins. The phosphodiesterase inhibitor methylisobutylxanthine (0.5 mM) had generally minor effects on 32P labeling; however, it did counteract the effects of NaNO2 on group I protein phosphorylation. Our results provide strong support for the hypothesis that TSH-dependent phosphorylation of group I proteins is mediated by cAMP, but they provide little evidence of cGMP regulation of histone or HMG protein phosphorylation.

Effects of cycloheximide, alpha-amanitin, and alpha-difluoromethylornithine on thyrotropin-induced increases in the micrococcal nuclease sensitivity of thyroid nuclear chromatin

Treatment of calf thyroid slices with TSH increases the nuclease sensitivity of nuclear chromatin, i.e. the amount of DNA released from nuclei by mild digestion with DNase I and micrococcal nuclease. Cycloheximide and alpha-amanitin were used to investigate the roles played by protein and RNA synthesis in mediating this effect of TSH; alpha-difluoromethylornithine, an irreversible inhibitor of ornithine decarboxylase, was used to investigate the possible involvement of polyamines. Calf thyroid slices were incubated with or without TSH (50 mU/ml) for 5 h, in the presence or absence of inhibitors. Nuclei were then prepared, subjected to mild digestion with micrococcal nuclease, and centrifuged at 1200 X g. The amount of DNA in 1200 X g supernatants was increased by TSH; this was inhibited by cycloheximide (100 micrograms/ml) and alpha-amanitin (4 micrograms/ml) when these agents were present throughout incubations with TSH. In contrast, alpha-amanitin failed to inhibit the TSH effect when it was added to incubations 30 min or 2 h after the addition of TSH. These results indicate that RNA and protein synthesis play a part in mediating the effect of TSH on the micrococcal nuclease sensitivity of chromatin, and that the RNA synthesis involved takes place within the first 30 min of exposure of thyroid slices to TSH. alpha-Difluoromethylornithine (5 mM) inhibited the TSH-dependent development of micrococcal nuclease sensitivity; however, it also inhibited nuclease digestion when it was added directly to nuclei prepared from fresh thyroid tissue. This observation should serve as a warning against uncritical acceptance of the notion that all effects of alpha-difluoromethylornithine are the result of inhibition of ornithine decarboxylase.

Synapse formation among developing sensory neurones from rat nodose ganglia grown in tissue culture

Sensory neurones from new-born rat nodose ganglia were grown in tissue culture, either with or without the ganglionic satellite cells, in order to investigate influences of satellite cells on sensory neurone development. To learn more about the post-natal development of nodose ganglia in rats neuronal counts of the ganglion were made at three different developmental stages. There were no significant differences of neuronal number in nodose ganglia in new-born rats, rats 3 weeks of age, and adult rats. Up to 60% of the neurones formed synapses with each other when they developed in culture without ganglion satellite cells. Pharmacological experiments indicated that the transmitter at these synapses was ACh and the post-synaptic receptors were nicotinic. Neurones co-cultured with satellite cells rarely formed functional synapses and most (85%) were not sensitive to ACh: 75% of neurones cultured without satellite cells were ACh sensitive. These results provide evidence that mammalian sensory neurones form synapses among each other in culture. The results also suggest that ganglionic satellite cells prevent functional synapses among these neurones from occurring, in part because the neurones do not express ACh sensitivity when co-cultured with satellite cells.

Growth faltering lacks association with the distribution of first year deaths

A retrospective study of infant mortality from death registers was made in St Lucia and St Vincent. In both islands postneonatal deaths by month were found to be evenly distributed throughout the first year although the total infant mortality rates differed widely. The growth of a cohort of children from three St Lucian villages was studied. Their weight curve showed 'faltering' at 3 months, closely resembling the developing world pattern described by Waterlow, Ashworth & Griffiths (1980). We therefore conclude that there is no necessary association between this pattern of infant growth and infant mortality rate, nor between the distribution of weight velocity and the distribution of deaths in the first year.

Thyrotropin-stimulated phosphorylation of high mobility group protein 14 in vivo at the site catalyzed by cyclic nucleotide-dependent protein kinases in vitro

Thyrotropin (TSH) treatment of bovine thyroid slices increased 32P-labeling of chromosomal high mobility group 14 (HMG) protein approximately 2-fold. Analogs of cAMP, but not cGMP, also enhanced phosphorylation of HMG 14. The sites of phosphorylation were analyzed by partial acid hydrolysis and by two-dimensional mapping of tryptic digests of 32P-labeled HMG 14 which was purified from control and TSH-treated thyroid tissue. TSH treatment enhanced phosphorylation at serine residues in four prominent tryptic phosphopeptides which were identical with those derived from HMG 14 phosphorylated in vitro with cAMP- and cGMP-dependent protein kinases. The four tryptic phosphopeptides contain serine 6, the major site of in vitro phosphorylation catalyzed by cyclic nucleotide-dependent protein kinases (Walton, G. M., Spiess, J., and Gill, G. N. (1982) J. Biol. Chem. 257, 4661-4668). TSH did not affect phosphorylation of serine 24, a minor site of phosphorylation in vitro. These studies suggest that TSH-stimulated phosphorylation of HMG 14 is catalyzed by cAMP-dependent protein kinase.

Familial nasopharyngeal carcinoma

We report 3 cases of nasopharyngeal carcinoma occurring in a single family group. All 3 patients are male, caucasian, born in Australia and of Greek origin. Two of the patients are brothers, the third their first cousin.

HMG (high-mobility-group)-14/17-like proteins in calf thyroid. Thyrotropin-dependent phosphorylation and comparison with calf thymus proteins

Two-dimensional polyacrylamide-gel electrophoresis of acid extracts of thyroid and thymus tissue, and of thyroid nuclei, revealed the presence of three HClO4-soluble nuclear proteins, PS.1, PS.2 and PS.3, whose electrophoretic mobilities closely resembled those of HMG (high-mobility-group) proteins 14 and 17. PS.1 co-migrated with HMG 14 on CM-Sephadex column chromatography. Like HMG 14, PS.2 and PS.3 were phosphorylated in calf thyroid slices; 32P-labelling of PS.3 was stimulated by thyrotropin. Thyrotropin also induced a rapid increase in the labelling of A5, an HMG-14/17-like protein found in whole calf thyroid and thymus tissue, but not in thyroid nuclei.

Pertussis: herd immunity and vaccination coverage in St Lucia

In a single complete epidemic in St Lucia, an island too small to support constant clinical pertussis, the pertussis case rates in small communities (villages and small towns) with differing levels of vaccination coverage of young children were compared. The association between greater vaccination coverage and greater herd immunity was clear, despite the imperfect protection given to individuals. An analysis in terms of population dynamics is evidence against the theory that endemic subclinical pertussis maintains transmission in a highly vaccinated population. We suggest that with a homogeneous vaccination coverage of 80% of 2-year-old children pertussis might be eradicated from the island, and that this is a practicable experiment.

Thyroxine, 3,5,3' -triiodothyronine and 3,3', 5' -triiodothyronine in human amniotic fluid: relationships between concentrations and turnover

We have made estimates of the possible contributions of various routes of entry and disposal to the turnover of thyroxine (T4), 3,5,3'-triiodothyronine (T3) and 3,3',5'-triiodothyronine (reverse T3, rT3) in human amniotic fluid (AF). Our calculations suggest that, in normal pregnancy, AF T4 and T3 are derived mainly from the maternal circulation, and that their concentrations depend very largely on binding-protein concentrations. The majority of AF rT3 is unlikely to enter the amniotic sac directly from the maternal circulation, or from the fetal circulation by passive diffusion or fetal urinary excretion; however, our calculations are consistent with the hypothesis it is derived largely from inner-ring deiodination of T4 in the fetal membranes. We propose that the molar ratio of one AF iodothyronine to another may yield more information about fetal thyroid status than the total concentration of any single iodothyronine.