Ergasilid copepods (Poecilostomatoida) from the gills of primitive Mugilidae (grey mullets)

All representatives of the subfamily Agonostominae of grey mullets in the collections of The Natural History Museum in London were examined for parasitic copepods. Agonostomus monticola, Joturus pichardi, Aldrichetta forsteri and Cestraeus goldiei. Three new species of Acusicola and two new species of Ergasilus were found: E. parabahiensis n. sp. on A. monticola from Guyana and E. acusicestraeus n. sp. on C. goldiei from Papua New Guinea. Acusicola spinuloderma n. sp. was found on A. monticola and J. pichardi collected from different localities in Central America, A. mazatlanesis n. sp. on the same host from West Mexico (Mazatlan) and A. joturicola n. sp. on J. pichardi from Panama. Descriptions of E. australiensis Roubal, from Aldrichetta forsteri, are presented. The host-parasite relationships and geographical distributions of hosts and their parasitic copepods are analyzed. (AU)

Scanning electron microscopy of the jejunum in children with protein-energy malnutrition

Samples of jejunum from seven children dying from severe oedematous malnutrition were fixed with intralumenal glutaraldehyde in combination with external immersion, using a rapid autopsy protocol. Selected areas were post-fixed in osmium tetroxide, dehydrated with an ethanol series and critical point dried. After mounting on aluminium stubs, specimens were sputter-coated with a thin layer of gold and palladium. Scanning electron microscopy showed patterns ranging from subtotal villous atrophy, through partial villous atrophy with low ridges, to longer, taller ridges with cerebriform convolutions. In one case, villous height had been interpreted as normal on light microscopy. The scanning electron microscope revealed that the mucosa in this case was composed of ridges and leaf forms. Processing for scanning electron microscopy is simple. The specimens can be viewed and photographed in a relatively short time. In addition, the three-dimensional record provides clarification of ambiguities which often arise from routine histological sections. (AU)

Electron microscopy in Jamaica: applications and techniques

Although the electron microscope was developed about 60 years ago in Germany, its arrival and subsequent use in Jamaica are of considerably more recent date. In this paper, the principles of scanning and transmission electron microscopy (SEM & TEM) are briefly explained, and examples are given of the research done with the electron microscopes at the University of the West Indies (UWI), Mona Campus, Jamaica, especially over the last three years. Detailed descriptions of specimen preparation are provided for both SEM and TEM and particular emphasis is placed on the methodology used in our laboratory, as it sometimes differs from the routine followed in electron microscopy units of temperate countries. (AU)

Ultrastructural and neuropharmacological findings in the nerve/muscle system of a digenean (Cercaria caribbea LXXI Cable)

The surface morphology and organization of the neuromuscular system in Cercaria caribbea LXXI are investigated using scanning and transmission electron microscopy, respectively. Direct and indirect (sarconeural) nerve-muscle junctions are identified in the cercarial tail. Synaptic vesicles at the direct neuromuscular junction suggest cholinergic and aminoacidergic transmission. Those at the sarconeural junctions suggest catecholaminergic and/or serotonergic transmission. Acetylcholinesterase and non-specific cholinesterases were found in high concentrations in the proximal and distal tail. Flourescence histochemistry showed primary catecholamines and 5-HT in the body and tail. 5-HT in the tail may represent a slowly depleted store, perhaps associated with energy availability and utilization. (AU)

The neurophysiological control and photosensory modulation of swimming in a cercaria, Cercaria caribbea LXXI

Scanning and transmission electron microscopy revealed that Cercaria caribbea LXXI has a small body (70 æm) with a pair of well-developed, rhabdomeric photoreceptors; and a large tail (4 mm) with six longitudinal, striated muscle bands. Muscle cells had an outer myofibrillar region adjecent to the tergument and an inner sarcoplasmic region, prolongations of which, may form sarconeural junctions. Sarcomere lengths were consistent with invertebrate fast muscle fibres. Diffuse Z-bands and the presence of numerous mitochondria are consistent with slow muscle fibres, adapted for prolonged work output. Interneuronal junctions with abundant electron-lucent and electron-dense vesicles, and neuromuscular junctions with mainly electron-lucent presynaptic vesicles were demonstrated. The neuromuscular connection between the body and tail appeared to be restricted to a single axon, implying that modulation of tail activity by the body may involve simple triggering or level setting actions, rather than complex modulation. The Falck-Hillarp Formaldehyde-Induced Fluorescence and the Gomori techniques indicated that the neuromuscular system utilizes primary catecholamines, serotonic (5-HT) and an acetylcholine-like transmitter. There were indications that 5-HT promotes activity and is held as a non-replenishable store, depleted through time within the cercarial tail. Exogenous application of a range of neuropharmacological agents, profoundly affected survivorship of the organism. Of the catecholaminergis group, propranolol (1.1-4 æM) and haloperidol (0.066-0.133 mM) most effectively reduced population half-line (T50). This was followed by the cholinergic agent, physostigmine (0.08-2.5 mM). The gamma-aminobutyric acid antagonist, picrotoxin (0.08-2.5mM), only weakly affected T50. Several drugs, especially reserpine (0.08-2.5mM), produced osmotic disturbances, leading to shortened life span. Survivorship was also dependent on pH, with a sharply defined tolerance range between pH 6 and 8. Suction electrodes recordings of electrical activity in the tail revealed spontaneous spike potentials (0.2-0.6 mV, 15-20/sec) superimposed on an underlying slow wave component. The effects of drugs on this activity were observed. 5-HT increased the amplitude and frequency of spike discharge from 0.2 mV to 0.8 mV and 15/sec to 25/sec, respectively. Physostigmine was the most effective reducer of both parameters. Indications were that cholinergic receptors in the nerve network may be excitatory nicotinic and inhibitory muscarinic. Excitatory beta adrenergic and inhibitory dopaminergic influences were observed. C. caribbea LXXI exhibited strong positive phototaxis. In response to light stimuli, the pigmented cercariae gave a maintained receptor potential with a small transient component. In the non-pigmented strain of C. caribbea LXXI, the photosensory receptor potential showed a large transient and a small maintained component. Drugs did not alter the photosensory response. A drug-induced decrease in linear translation towards a photic stimulus was therefore due to a disturbance in the neuromuscular system (AU)

Scanning electron microscopy of proliferating bile ductules

Rats were subjected to ligation of the common bile duct to provoke bile ductular proliferation and were studied at intervals from 1 day to 6 weeks. After perfusion fixation with glutaraldehyde, and ethanol dehydration, blocks of liver were frozen in liquid nitrogen, fractured, and returned to ethanol prior to critical point drying. Examination with the scanning electron microscope showed a remarkable proliferation of bile ductules and preductules in addition to canalicular dilation. The ductules were surrounded by a longitudinal array of collagen fibers. The luminal surfaces contained many microvilli and cable-like structures, some identifiable as cilia by transmission electron microscopy. The present techniques offer the possibility for a reevaluation of obstructive jaundice and cholestasis.(AU)

Scanning electron microscopy of rat's liver: application of freeze-fracture and freeze-drying techniques

Portal vein perfusion of rat's liver was carried out with Ringer's solution followed by 2.5 per cent glutaraldehyde. Liver samples were postifixed in osmium tetroxide, washed in distilled water, snap-frozen in Freon-12, and fractured at -150§C. After freeze-drying at -80§C., a thin layer of carbon and gold was applied under vacuum. Under the scanning electron microscope, the sinusoidal fenestrations and the relationships of the endothelial cells to hepatocyte microvilli and reticulin fibres were delineated. Images of bile canaliculi and adjoining plasma membranes were obtained. These techniques have great potential for the study of a variety of liver diseases. (AU)