Effects of Muscarinic Agonists and Depolarizing Agents on Inositol Monophosphate Accumulation in the Rabbit Vagus Nerve

The effects of muscarinic agonists and depolarizing agents on inositol phospholipid hydrolysis in the rabbit vagus nerve were assessed by the measurement of [3H]inositol monophosphate production in nerves that had been preincubated with [3H]inositol. After 1 h of drug action, carbachol, oxotremorine, and arecoline increased the inositol monophosphate accumulation, though the maximal increase induced by these agonists differed. Addition of the muscarinic antagonists atropine or pirenzepine shifted the carbachol dose-response curves to the right, without decreasing the carbachol maximal stimulatory effects. The KB for pirenzepine was 35 nM, which is characteristic of muscarinic high-affinity binding sites coupled to phosphoinositide turnover and often associated with the M1 receptor subtype. On the other hand, agents known to depolarize or to increase the intracellular Ca2+ concentration, e.g., elevated extracellular K+, ouabain, Ca2+, and the Ca2+ ionophore A23187, also increased inositol monophosphate accumulation. These effects were not mediated by the release of acetylcholine, as suggested by the fact that they could not be potentiated by the addition of physostigmine nor inhibited by the addition of atropine. The Ca(2+)-channel antagonist Cd2+, also known to inhibit the Na+/Ca2+ exchanger, was able to block the effects of K+ and ouabain, but did not alter those of carbachol. These results suggest that depolarizing agents increase inositol monophosphate accumulation in part through elevation of the intracellular Ca2+ concentration and that muscarinic receptors coupled to phosphoinositide turnover are present along the trunk of the rabbit vagus nerve.     

Renal function and plasma arginine vasotocin during an acute salt load in feral chickens

Summary Renal clearance experiments were conducted on feral chickens descended from birds collected from a coral island off the coast of Queensland, Australia. Following a control period when 0.13 M NaCl was used as a vehicle for the renal function markers, a salt load was imposed by infusion of 1 M NaCl. The hypertonic NaCl infusion resulted in increases in glomerular filtration rate (GFR), effective renal blood flow (ERBF), and urine flow rate (V), whereas filtration fraction decreased. Haematocrit was reduced and plasma osmolality, sodium, chloride and potassium concentrations increased. Plasma arginine vasotocin (P_AVT) levels increased from 31.4±2.3 pg·ml^-1 during the control infusion to 56.0±1.7 pg·ml^-1 following a salt load of 12 mmol Nacl·kg^-1 The sensitivity of release of AVT was 0.69±0.11 pg·ml^-1 per mosmol·kg^-1. The concentrations of Na and Cl in urine increased, whereas urine osmolality and potassium concentration decreased. The expansion of the extracellular fluid volume induced by the salt loading would tend to suppress the release of AVT, whereas the osmotic stimulus would provide a stimulus for the release of AVT. In this study, GFR, ERBF and ERPF increased at the same time as P_AVT increased.Abbreviations AVP arginine vasopressin - AVT arginine vasotocin - ERBF effective renal blood flow - ERPF effective renal plasma flow - GFR glomerular filtration rate - P_avt plasma arginine vasotocin concentration - PAH paraaminohippuric acid - SEM standard error of mean - SNGER single nephron glomerular filtration rate - U/P urine to plasma ratio - V urine flow rate     

Morphogenesis of the renal juxtaglomerular apparatus and peripolar cells in the sheep

Summary The morphogenesis of the juxtaglomerular apparatus and peripolar cells was studied in the metanephros of fetal sheep (from 24 to 147 days of gestation) using light and electron microscopy. The first juxtaglomerular apparatus was detected at 45 days of gestation, following constriction of the edges of Bowman's capsule and formation of the vascular pole of the renal corpuscle. Mesenchymal cells gave rise to lacis cells and to smooth muscle and epithelioid cells of the juxtaglomerular arterioles. Epithelioid cells developed only sparse cytoplasmic granulation, first detectable at 92 days. The macula densa developed from tubular cells at the junction of the middle and upper limbs of the S-shaped body of the developing nephron. Peripolar cells arose from epithelial cells in the lower limb of the S-shaped body, at the constricting edges of Bowman's capsule, and formed a cuff around the origin of the glomerular tuft. Cytoplasmic granules were first detected in peripolar cells at 53 days, and remained more prominent than epithelioid cell granulation throughout gestation.     

Catabolism of Endogenous Dopamine in Peripheral Tissues: Is There an Independent Role for Dopamine in Peripheral Neurotransmission?

Abstract: Dopamine (DA) and its metabolites, homovanillic acid (HVA) and 3,4-dihydroxyphenylacetic acid (DOPAC), have been measured in peripheral tissues of the rat and human by gas chromatography-mass spectrometry. The content of HVA and DOPAC in peripheral tissue is higher than in blood and is usually higher than the content of DA. In the rat, chemical denervation with 6-hydroxydopamine decreased the tissue content of DOPAC. inhibition of monoamine oxidase increased tissue DA. Apparently, in vivo , a large quantity of peripheral DA is catabolized rather than converted to norepinephrine (NE). These observations suggest that either NE synthesis is inefficient, with a large quantity of DA wasted and not converted to NE, or that DA is physiologically utilized as a neurotransmitter and/or cotransmitter in many peripheral nerves. A survey of the reported actions of DA on peripheral tissues suggests that the latter proposal is more likely.     

Chloride distribution in the proximal convoluted tubule ofNecturus kidney

Summary To assess the mechanism(s) by which intraluminal chloride concentration is raised above equilibrium values, intracellular Cl^– activity ( _i ^Cl ) was studied in the proximal tubule ofNecturus kidney. Paired measurements of cell membrane PD (V _BL) and Cl-selective electrode PD (V _BL ^Cl ) were performed in single tubules, during reversible shifts of peritubular or luminal fluid composition. Steadystate _i ^Cl was estimated at 14.6±0.6 mmol/liter, a figure substantially higher than that predicted for passive distribution. To determine the site of the uphill Cl^– transport into the cell, an inhibitor of anion transport (SITS) was added to the perfusion fluid. Introduction of SITS in peritubular perfusate decreased _i ^Cl , whereas addition of the drug in luminal fluid slightly increased _i ^Cl ; both results are consistent with basolateral membrane uphill Cl^– transport from interstitium to the cell. TMA⁺ for Na⁺ substitutions in either luminal or peritubular perfusate had no effect on _i ^Cl . Removal of bicarbonate from peritubular fluid, at constant pH (a situation increasing HCO ₃ ^– outflux), resulted in an increase of _i ^Cl , presumably related to enhanced Cl^– cell influx: we infer that Cl^– is exchanged against HCO ₃ ^– at the basolateral membrane. The following mechanism is suggested to account for the rise in luminal Cl^– concentration above equilibrium values: intracellular CO₂ hydration gives rise to cell HCO ₃ ^– concentrations above equilibrium. The passive exit of HCO ₃ ^– at the basolateral membrane energizes an uphill entry of Cl^– into the cell. The resulting increase of _i ^Cl , above equilibrium, generates downhill Cl^– diffusion from cell to lumen. As a result, luminal Cl^– concentration also increases.C.N.R.S. Greco 24. Part of this work was presented at the 12^th annual meeting of the American Society of Nephrology, Boston, Mass. (Edelman et al., 1979).     

Dopamine and Noradrenaline Levels in Peripheral Tissues of Several Mammalian Species

Abstract: Tissue levels of dopamine (DA) and noradrenaline (NA) have been compared in atrium, spleen, mesenteric artery, vas deferens and renal cortex of sexually mature rats, guinea-pigs, ferrets, rabbits and cats. The results suggest the presence of dopaminergic autonomic axons in the cat renal cortex, as has been previously reported for the dog. Such nerves are probably sparse or absent in the kidneys of the other species examined.     

Central projections of fibers in the auditory and tensor nerves of cicadas (Homoptera: Cicadidae)

Summary The auditory and tensor nerves of cicadas are mixed nerves containing both afferent and efferent elements. In 17-year cicadas, and in Okanagana rimosa, the auditory nerve contains afferents from body hairs, from the detensor tympani-chordotonal organ, and some 1300–1500 afferents from the hearing organ. Within the fused metathoracic-abdominal ganglionic complex the receptors from both the auditory and tensor nerves form a neuropilar structure that reveals the metameric organization of this complex. A few fibers run anteriorly, projecting into the meso and prothoracic ganglia. Within the ganglionic complex a division of auditory nerve afferents into a dense intermediate and a more diffuse ventral neuropile is observed. In addition, a dorsal motor neuropile is outlined by arborizations of the timbal motor neuron. This neuron is one of several efferent cell types associated with the auditory nerve, and there is an indication that several efferent fibers innervate the timbal muscle. There is anatomical evidence for a possible neuronal coupling between the bilaterally symmetrical large timbal motor neurons. In general, central projections from the auditory and tensor nerves support evidence of a structural layering within the CNS of insects.     

The ultrastructure of paraganglia associated with the inferior mesenteric ganglia in the guinea-pig

Summary The paraganglia of the inferior mesenteric ganglia in the guinea-pig are composed of small chromaffin cells containing an abundance of granule-containing vesicles. The chromaffin cells are almost completely surrounded by satellite cells. In areas in which satellite cell processes do not intervene, the membranes of adjacent chromaffin cells are closely apposed and often form specialized attachment zones. The paraganglia contain a dense capillary network, the endothelial cells of which are often extremely attenuated and show areas of fenestration. The processes of chromaffin cells approach close to the capillary walls and are often bare of satellite cells covering on the side facing the capillary. Evidence has been obtained for the exocytotic release of the contents of chromaffin cell vesicles into pericapillary spaces. Synapses of cholinergic and noradrenergic axons are seen on the chromaffin cells. The cholinergic axons degenerate when the praganglia are decentralized, but the noradrenergic axons, which appear to arise from the local inferior mesenteric ganglia, remain intact. The results suggest that the paraganglia have an endocrine function.     

Fluorescence-microscopical demonstration of a population of gastro-intestinal nerve fibres with a selective affinity for Quinacrine

Summary A population of nerve fibres in the gastro-intestinal tract of mice showing a high affinity for quinacrine was revealed by fluorescence microscopy. Similar results were obtained in rats and guinea pigs. Whole-mounts of sheets of the smooth muscle layer following incubation in 10^-6-10^-7 M quinacrine for 15–60 min revealed fine fluorescent varicose nerve fibers in the myenteric plexus of Auerbach both around nerve cell bodies and in the interconnecting strands. Many fibers were also present between the strands of the plexus, especially running parallel to the circular muscle layer. Such fibers were not seen in similarly quinacrine-incubated irides. A proportion of the cell bodies in Auerbach's plexus also showed quinacrine accumulation. These cells were apparently smaller neurons, sometimes with fluorescent processes. Intraperitoneal injections of quinacrine failed to demonstrate nerve fibers, but some cell bodies in Auerbach's plexus were positive. Subsequent paraformaldehyde treatment for monoamine visualization showed persistent adrenergic nerve terminals in the intestine and iris. These nerves seemed to be fewer and had a more yellow fluorescence than normally. The identity of the quinacrine-positive fibers is discussed with respect to recent suggestions that purinergic, substance P, enkephalin, and somatosin-containing nerves, in addition to adrenergic and cholinergic nerves, are present in the gut wall.Supported by the Swedish Medical Research Council (04X-03185). Magnus Bergvalls Stiftelse and Karolinska Institutets Fonder. For generous gifts of Mepacrine we thank Winthrop, Skärholmen, Stockholm, Sweden. The skilful technical assistance of Miss Gerd Boetius and Miss Maud Eriksson is gratefully acknowledged     

New sense organ in larval hookworms.

A new ciliary sense organ is described which is bilaterally arranged, one in each lateral cord. It is just posterior to the nerve ring and adjacent to the excretory duct. The cilium is closely associated with another structure which is itself connected to the cuticle beneath the lateral alae. A nervous circuit is proposed which links this receptor via the hemizonid to the nerve ring. The receptor and associated structures are in the infective larvae of Necator americanus and Ancylostoma tubaeforme.