The effects of Heterosigma akashiwo on juvenile Oncorhynchus tshawytscha and its implications for fish culture

The effects of natural blooms of Heterosigma akashiwo on freshwater-and saltwater-acclimated juvenile chinook salmon were assessed. Rates of fish mortality in the blooms were independent of acclimation of fish to seawater and the ambient oxygen levels, but were dependent on concentration of algae and ambient water temperatures. No pathological abnormality to gills or other internal organs in the fish were evident. Aeration or oxygenation of fish cages did not enhance or inhibit fish survival in a H. akashiwo bloom. Cause of death was considered to be due to a labile ichthyotoxic agent.     

Two acceptor sub-types for dendrotoxin in chick synaptic membranes distinguishable by beta-bungarotoxin

Using chick synaptic membranes, proteinaceous acceptors were characterized for dendrotoxin, a polypeptide from Dendroaspis angusticeps with convulsant activity due to its facilitation of transmitter release, resulting from inhibition of A-current K+ channels in brain. Both equilibrium and kinetic measurements of radioiodinated toxin binding showed that two populations of membraneous acceptors were discernible with different affinities (Kd approximately 0.5 nM and 15 nM; Bmax approximately 90 and 400 fmol/mg protein). Only the high-affinity component interacted avidly with beta-bungarotoxin, an inhibitory presynaptic neurotoxin whose lighter chain is homologous to dendrotoxin. Facilitatory homologues of dendrotoxin from Dendroaspis species antagonised its binding to both acceptor sub-types in proportion to their central neurotoxicities, whereas various other toxins (crotoxin, apamin), trypsin inhibitors and lectins proved ineffective. Cross-linking of toxin specifically bound to its membrane acceptors, using bis-imido esters followed by electrophoretic analysis in the presence of sodium dodecyl sulphate, revealed a polypeptide with Mr of 75,000 together with lesser amounts of a 69,000-Mr component. Notably, the covalent labelling of each of these bands was inhibited partially by low concentrations of beta-bungarotoxin, indicating that they are derived from both acceptor species. The demonstrated existence of an acceptor form shared by dendrotoxin and beta-bungarotoxin, together with another sub-type selective for dendrotoxin, is discussed in relation to the known pharmacological interactions of these toxins which exert opposite effects on transmitter release.     

MYELOGRAPHY—Diagnostic Value in Lesions of the Lumbar Intervertebral Discs with a Variation in Technique

Myelography using pantopaque in greater than usual amount with a variation in technique, which is described, is believed to provide increased accuracy in differential diagnosis and precise localization of lesions in the lumbar spine. The need for multiple space exploration is eliminated and more detailed information concerning the size and shape of lesions is provided as compared to that secured by the use of 3 or 6 cc. of opaque medium and fluoroscopic examination alone. In 53 cases in which lumbar myelography was performed and the diagnosis verified or disproved at operation, there was a 5 per cent diagnostic error in 41 instances in which the method outlined was used, as compared with 17 per cent error in 12 cases in which only 3 or 6 cc. of radiopaque material and fluoroscopy alone were used. The accuracy of the procedure would appear to warrant its use in the evaluation of patients suspected of having abnormalities of the lumbar discs associated with nerve root compression.     

Laparoscopy and Gonadal Biopsy for Assessment of Gonadal Function in Primary Amenorrhoea

Twenty patients with primary amenorrhoea have been investigated by laparoscopy and gonadal biopsy, endocrine and chromosomal studies. Laparoscopy and gonadal biopsy made the major contribution to the diagnosis, prognosis, and management of the patients and provided a method for study of the functional anatomy of the ovary.