An analysis of axon caliber within the optic nerve of the cat: evidence of size groupings and regional organization

Axon size in the optic nerves of three adult cats was measured using an accurate planimetric method. A sample of the axon complement was obtained from sets of more than 125 electron micrographs taken at each nerve. In contrast to previous reports, the distribution of axon diameter, as estimated from measurements of axonal cross-sectional area was clearly bimodal. The group of finest axons had a mode at approximately 1 micrometer, and the mode of the group of intermediate size axons was approximately 2 micrometers. Fibers with diameters larger than 3.5 micrometers formed the extensive tail of the distribution. The proportions of large, intermediate, and small axons were estimated to be 5%, 45%, and 50%. These groups probably correspond to the alpha, beta, and gamma classes of retinal ganglion cells. Regional distributions of axon caliber were also bimodal and, in a few instances, even trimodal. A peripheral crescent of each nerve contained a large number of fine fibers. Mean fiber diameter within discrete regions of the optic nerve varied inversely with the density of axon packing. The thickness of the myelin sheath was highly correlated with the inner fiber diameter, hence, myelin sheath width was also distributed in a bimodal manner. These results furnish the first clear evidence that the distribution of fiber caliber within the cat's optic nerve mirrors the principal classes of retinal ganglion cells.

Estimation of protein secondary structure from the laser Raman amide I spectrum

A new method for estimating protein secondary structure from the laser Raman spectrum has been developed whereby the amide I Raman band of a protein is analyzed directly as a linear combination of amide I bands of proteins whose secondary structures are known. For 14 proteins, analyzed by removing each one from the reference set and analyzing its structure in terms of the remaining proteins, the average correlation coefficients between the Raman and X-ray diffraction estimates of helix, beta-strand, turn, and undefined were 0.98, 0.98, 0.82 and 0.35, respectively. Significant correlations were also observed for distinctions between alpha-helix (0.98) and disordered helix (0.82), and between parallel (0.82) and antiparallel (0.97) beta-sheets. The average standard deviation of these Raman estimates from the X-ray values is less than 4%. In addition, a singular value analysis of 20 Raman amide I spectra indicates that there may be as many as nine significant independent pieces of information present in the amide I region.

The exchange of calcium in larvae of the mosquito Aedes aegypti

The exchange of labelled calcium between the external medium and the whole body was investigated in the larva of Aedes aegypti (L.) using a closed, two-compartmental model. The transport system for the uptake of Ca2+ was found to be saturable and obeyed Michaelis-Menten kinetics. The efficiency of the inward transport of calcium from dilute solutions was markedly reduced by starvation or by ruthenium-red, a selective inhibitor of Ca2+ activated ATPase, indicating that this transport system is energy dependent. Unlike transport systems for the major monovalent ions, the Ca2+ transport system is not located in the anal papillae, since removal of these organs resulted in enhanced Ca2+ fluxes. While over 95% of the calcium in the larva appeared to be distributed in the extracellular haemolymph, only 16% of the total calcium was readily exchangeable with the external medium; thus the majority of the calcium is apparently bound to haemolymph constituents. The results suggest that calcium pumps consisting of Ca2+ activated ATPases play an important role in the absorption of Ca2+ from dilute solutions in the gut and its reabsorption from the urine in the rectum.

Loss of axons in the cat optic nerve following fetal unilateral enucleation: an electron microscopic analysis

Between the 48th day of gestation (E-48) and maturity, the number of axons in the cat optic nerve is reduced by approximately 50%. On the basis of an electron microscopic assay, the axon population of the E-48 nerve was estimated to be 328,000. In contrast, estimates from two normal adults were 159,000 and 158,000. In utero unilateral enucleation (at E-45 and E-46) attenuated the severity of this loss since the optic nerves of the experimental animals contained 200,000 and 198,000 fibers. These results indicate that prenatal binocular competition is involved in the elimination of ganglion cell axons during the normal development of the cat's visual system. The increased number of axons in the optic nerve of the prenatally enucleated animals could be due to reduced ganglion cell death or a failure to retract supernumerary axon collaterals. It is suggested that the former explanation is more consistent with what is currently known about the development of retinofugal projections.

Raman spectroscopy of avidin: secondary structure, disulfide conformation, and the environment of tyrosine

An analysis of the amide I region of Raman spectra indicates that avidin has 10 +/- 5% and 55 +/- 4% of its residues in helical and beta-strand conformations, respectively. Predictions of secondary structure on the basis of the sequence of avidin are consistent with the high percentage of residues in the beta conformation. We observe no differences between the spectra of avidin in solution and in crystals nor is there a significant difference between the secondary structures of avidin and the complex of avidin with biotin. In addition, the ratio of the intensities of the tyrosine doublet at 826 and 855 cm-1 indicates the lone tyrosine side chain of an avidin subunit is in a strong hydrogen bond as a proton acceptor. The Raman data also indicate the single disulfide of an avidin subunit has dihedral angles of 0-50 degrees for each of its two C beta-S bonds and a dihedral angle of 85 +/- 20 degrees for its disulfide bond. We discuss the significance of these results in relation to findings of earlier work on avidin.

Prenatal development of retinocollicular projections in the cat: an anterograde tracer transport study

The retinal projection to the superior colliculus of the cat was examined at four gestational ages, embryonic days 38, 46, 56, and 61, using the antegrade transport of horseradish peroxidase and tritiated leucine. Gestation in the cat averages 65 days. By the 38th day of gestation (E38), the anlage of the entire superior colliculus, both ipsilateral and contralateral to an injection, was labeled intensely. The peroxidase label had an extremely coarse grained texture. As late as E46, the ipsilateral retinal projection extended to the presumed caudal border of the colliculus, while by E56, as in the mature cat, the ipsilateral terminal field was largely excluded from the rostral and caudal tectal poles. The contralateral terminal field at E56, as in younger fetal material, extended across the entire tectal mantle. By E61, clear gaps of label were observed in the contralateral stratum griseum superficiale. At this age, patches or bands of label were accentuated on the ipsilateral side. In double labeled tissue, it could be demonstrated that the ipsilateral patches corresponded quite closely to the gaps in the contralaterally derived label. Thus, a few days before birth, the retinal projection to the superior colliculus has a pattern which resembles that of the adult.

Lumbar discectomy--percentage of disc removal and detection of anterior annulus perforation

A prospective study was carried out to estimate the percentage of disc removal at the time of lumbar laminectomy and discectomy. Intraoperative discograms were obtained which afforded a method of calculating the percentage of disc removal. The technique permits localization of the level of discectomy and provides a means of detecting anterior annulus perforation intraoperatively, which we hope will reduce the morbidity of anterior annulus perforation. A comparison between the efficacy of disc removal (microdiscectomy vs. laminectomy) is also presented.

Ultraviolet and laser Raman investigation of the buried tyrosines in fd phage

The tyrosines of the filamentous phage fd have been found to be inaccessible to solvent by pH titration while monitoring the ultraviolet spectrum or the laser Raman spectrum. The uv spectra suggest that the tyrosines do not become deprotonated unless the phage becomes disrupted. One possible explanation of the Raman spectra is that the tyrosine OH groups are the recipients of hydrogen-bonded protons arising from fairly acidic donors, yet these acidic donors do not become titrated over the pH 7 to 12 range.

Laser Raman studies of lipid disordering by the B-protein of fd phage

Complexes of the B-protein of fd phage with the model lipid dipalmitoyl phosphatidylcholine (DPPC) were made by sonication of the fd phage in the presence of dipalmitoyl phosphatidylcholine. Both laser Raman spectra and circular dichroism show the protein in the membrane to be almost entirely in the beta-sheet conformation. This beta-sheet conformation is found to be independent of the temperature between 10 degrees C and 50 degrees C. On the other hand, the protein has a very dramatic effect on the organization of the lipid bilayer. An aqueous dispersion of 1 : 1 lipid/protein mixture gives a broad conformational transition of DPPC which occurs between 10 degrees C and 30 degrees C. This contrasts markedly with simple aqueous DPPC dispersions which show a sharp transition at 41 degrees C. This appears to be the first reported example of the lowering of the conformational transition of a membrane bilayer by an intrinsic membrane protein.

Experimental pancreatitis: Effect of plasma and dextran on pancreatic blood flow

In spite of extensive investigations, many aspects of the hemodynamic changes occurring in acute pancreatitis are understood poorly. A dog model was established in which continuous measurements of pancreatic arterial blood flow, cardiac output, and mean arterial blood pressure were made using electromagnetic flow probes and a pressure transducer, respectively. Pancreatitis was induced and the animals were monitored for 3 hours. In addition, control animals (group I) without pancreatitis also were done. All animals 50 ml of saline in the first hours. Three methods of therapy then were instituted in the dogs with pancreatitis and their effects were recorded. group I 6 dogs control animals no pancreatitis saline 50 ml/hr group II 10 dogs saline 50 ml/hr group III 6 dogs plasma 15 ml/kg over 45 min then saline 50 ml/hr group IV 10 dogs saline 50 ml and 1.5 ml/kg of dextran 40/hr These results confirm the observations made previously using a transillumination technique--that the pancreatic circulation rapidly reduces in acute pancreatitis. Administration of plasma produced a significant (P less than 0.05) but transient increase in the cardiac output and pancreatic blood flow; however, the blood pressure remained low. Dextran 40 minimally increased cardiac output, but it significantly improved the blood pressure and maintained the pancreatic blood flow. Low-dose, low-molecular weight dextran 40 appears to help to maintain pancreatic blood flow in acute pancreatitis. The possible mechanisms concerning the made of action of dextran 40 will be discussed.

Microlumbar discectomy: a conservative surgical approach to the virgin herniated lumbar disc

Microlumbar discectomy is an extremely conservative microsurgical procedure for the treatment of the virgin herniated lumbar disc. The technique has been utilized in 530 patients over a 5 1/2-year period, and features no laminectomy or curettement of the disc space. Preservation of extradural fat and blunt perforation of the annulus fibrosus, rather than scalpel incision, appear to minimize reherniations and adhesion reactions. Operating time has averaged 37 minutes and postoperative stay 3.1 days during the past 36 months (46% of these were compensation cases). In this series, a satisfactory result is defined as those patients who remain economically productive and physically comfortable at the time of followup. Satisfactory results were achieved in 91% of patients after one procedure.

Circular dichroism studies of fd coat protein in membrane vesicles

Circular dichroism studies on filamentous virus coat protein in lipid vesicles show that distinctive spectra result depending on the history of the protein and the method of vesicle preparation.

Mixed tumor of female breast of unusual duration and size

A 72-year-old black woman presented with huge enlargement of the right breast beginning approximately 30 years earlier and progressively enlarging over the years. The breast was stony hard, painless, and inconvenient only because of size and weight. Simple mastectomy was done and pathologic examination showed a benign mixed tumor with large areas of pseudocartilage, osteoid, and bone formation. Preoperatively the serum calcium was 11.0 mg/100 ml and alkaline phosphatase, 550 mU/ml (SMA-12). Postoperative course was uneventful and within several weeks the alkaline phosphatase fell to a normal range (35-115 mU/ml). The case presented requires little comment other than its unusual nature and duration. Extensive bone formation was undoubtedly responsible for the elevated alkaline phosphatase and, as expected, it returned to normal limits following excision of the tumor. Simple mastectomy is considered the treatment of choice.

Mass casualties in a maximum security institution

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Interruptions in single strands of the DNA in slime mold and other organisms

The molecular weight of single-stranded DNA from the slime mold Physarum polycephalum has been determined by alkaline gradient centrifugation. The average molecular weight during DNA synthesis ( approximately 1.5 x 10(7) D) is less than that observed in nonsynthetic periods ( approximately 4 x 10(7) D). On the basis of a chromosome number of 50 per nucleus and a DNA content of 1 mumug per nucleus, we are led to conclude that at pH 12 each chromosome dissociates into 300 (single-stranded) pieces of DNA. We have also compared the sedimentation profiles of single-stranded DNA from Escherichia coli, PPLO, and T2 bacteriophage. These data support the conjecture that each bacterial chromosome can be dissociated into 10 or 12 single-stranded pieces of DNA. Dissociation of DNA into multiple pieces under our experimental conditions is best interpreted in terms of interruptions in the continuity of the DNA either by naturally occurring gaps or at alkali-labile bonds.

Breakdown of DNA in x-irradiated Escherichia coli

A comparison of differences in incorporation and loss of radio-activity between two strains of Escherichia coli shows that: (a) three times as much irradiation is necessary to produce the same reduction in incorporation of H(3)-thymidine in B/r, the resistant strain, as in B(s - 1), the sensitive one; (b) radioactivity is lost from the DNA of previously labeled bacteria during the first few cell generations after X-ray exposure, and even though the initial rate of loss is similar for all strains, the sensitive one loses much more label; (c) loss of DNA is a complicated function of dose. Losses increase with dose up to 25 or 50 kr in both strains; with higher doses, losses decrease in B(s - 1) but are unchanged in B/r. Since in both strains labeled RNA is retained in irradiated cells, lysis has not occurred but the DNA is broken down into small pieces which leak from each cell. Losses from either strain do not occur at ice-bath temperature, indicating that breakdown is a function of metabolic processes. A proposed mechanism for X-ray damage and repair is advanced.