Neonatal neuronal loss in rat superior cervical ganglia: retrograde effects on developing preganglionic axons and Schwann cells

Summary Beginning prenatally and during the first week after birth, there is normally a loss of axons in rat cervical sympathetic trunk. To test the hypothesis that this spontaneous axonal loss represents a natural process whereby an excessive number of immature preganglionic axons in the cervical sympathetic trunk adapts to the neuronal population in the superior cervical ganglion, the number of nerve cells in the superior cervical ganglion was reduced in newborn rats by administration of nerve growth factor antiserum, 6-hydroxy-dopamine or postganglionic axotomy. Quantitative ultrastructural studies of these animals at later stages of development revealed that, with each method, the number of preganglionic axons and Schwann cells was reduced to nearly one-third of normal. These findings indicate that the superior cervical ganglion plays an important role in the development of the cervical sympathetic trunk. Removal of ganglionic cells causes a retrograde loss of preganglionic fibres. This process probably represents an exaggeration of the normal mechanism for elimination of redundant axons. Because the changes in axonal numbers are associated with similar reductions in the number of Schwann cells, it can also be concluded that postnatal Schwann cell proliferation is influenced by axonal populations.     

Experimental necrosis and arrest of proliferation of Schwann cells by cytosine arabinoside.

In developing rat cervical sympathetic trunks, Schwann cells proliferate intensely during the first week after birth but axonal populations do not increase. Thus, experimental inhibition of DNA synthesis should affect Schwann cells and spare axons whose cell bodies are not dividing. The present investigation was aimed at determining the effects of an inhibitor of DNA synthesis-cytosine arabinoside (ara-C)--on axons and Schwann cells in developing nerves. Ara-C (60 mg kg(-1) body weight) was injected subcutaneously to newborn rats every six hours for 36 hours. At intervals from 2--4 days of age, animals were given tritiated thymidine (4 muCi per gram body weight) to label Schwann cells in synthesis phase. One hour later rats were killed by systemic perfusion of phosphate buffered glutaraldehyde. Cervical sympathetic trunks (CST's) and sciatic nerves were removed and processed for radioautography and electron microscopy (EM). Labelled and unlabelled Schwann cell nuclei were counted to determine the labelling index (LI%) for each nerve. By the end of ara-C treatment there was almost complete absence of labelling but LI's rose sharply 24 hours after discontinuing ara-C. By EM axons appeared normal; Schwann cells, however, showed prominent nuclear and cytoplasmic changes consisting of nuclear degeneration, dilatation of rough endoplasmic reticulum and increased cytoplasmic density. Ara-C, by suppressing proliferation and causing necrosis of Schwann cells but sparing axons, results in a developmental alteration of axon-Schwann cell relationships. It is suggested that the pathogenetic mechanism involves an inbalance in DNA/RNA synthesis metabolism.     

Macronutrient diet intake of the lethal yellow agouti (Ay/a) mouse

To examine the effect of chronic endogenous melanocortin receptor (MC-R) antagonism on macronutrient diet selection, Ay/a mice that ectopically overexpress the MC-R antagonist, agouti, were fed a three-choice macronutrient diet of pure fat, carbohydrate, and protein. Ay/a mice gained more weight and consumed a greater proportion of their daily intake from fat and less from carbohydrate than wild-type littermates did. The increased fat preference was present immediately, and persisted throughout the 7-week long experiment. Protein intake was greater for Ay/a mice; however, the proportion of protein intake to total intake was similar between mouse types. Ovarian fat pads of Ay/a mice comprised a greater percentage of total body weight that that from wild-type littermates. These results suggest that endogenous inhibition of MC-Rs mediate the increased fat intake in growing mice.     

Evaluation of laser Doppler imaging to measure blood flow in knee ligaments of adult rabbits

Laser Doppler imaging (LDI) is investigated as a novel method for in vivo ligament tissue blood flow determination. LDI output signal is obtained from surgically exposed rabbit medial collateral ligaments (MCL). The LDI signal, is compared with simultaneously determined, coloured microsphere (CM)-derived standardised MCL blood flow. Correlation of LDI output with the CM flow data and a linear regression of 17 data points in nine rabbits (joint injured to provoke an acute vascular response in the tissues) indicate that LDI provides a reasonable estimate of MCL blood flow, at least over the ranges assessed. If properly calibrated, and given enough tissue-specific data points, LDI may have advantages over conventional, but more invasive, techniques. The potential clinical application of LDI technology to joint injury and arthritis research is discussed.     

T cells from patients successfully treated with OKT3 do not react with the T-cell receptor antibody

The mechanism of OKT3 therapy is complex and may include depletion of circulating CD3 cells, modulation of the CD3 molecule, and/or functional inactivation of T cells. Although the absolute number of circulating CD3 cells in OKT3-treated patients is used to monitor therapy, many laboratories assign CD3 numbers based on reactivity with OKT3. These CD3 numbers could be artificially low since the epitope recognized by OKT3 may already be occupied. Using a monoclonal antibody against a different CD3 epitope, we detected CD3 expression on T lymphocytes from 18/18 OKT3-treated patients. Nonetheless, OKT3 therapy in these patients was clinically successful, suggesting that monitoring patients solely for CD3 is uninformative. Since CD3 is associated with the T-cell receptor (TcR), we also evaluated alpha-TcR-1, a monoclonal antibody which detects a conformational determinant of the CD3/TcR alpha/beta complex, and found that less than 1% of the CD3 cells from OKT3-treated patients reacted. Furthermore, these cells were unresponsive to allogeneic stimulation. However, when patient cells were cultured overnight in the absence of OKT3, both alpha-TcR 1 binding and responsiveness to allogeneic stimulation became detectable. Thus, the monitoring of patients treated with OKT3 can be more informative if lymphocytes are tested for reactivity with alpha-TcR-1 and an alpha-CD3 antibody other than OKT3.     

In vivo comparison of scanning technique and wavelength in laser Doppler perfusion imaging: Measurement in knee ligaments of adult rabbits

At present, there are only two laser Doppler perfusion imaging systems (LDls) manufactured for medical applications: a ‘tepwise’ and a ‘continuous’ scanning LDI. The stepwise scanning LDI has previously been investigated and compared with coloured microsphere determined standardised flow. The continuous scanning LDI is investigated and compared with the stepwise scanning LDI for its ability to measure in vivo, hypoaemic, ligament tissue blood flow changes. The continuous scanning system was supplied with two lasers, red and near infrared (NIR), allowing for additional assessment of the effect of wavelength on imaging ligament perfusion. Perfusion images were obtained from surgically exposed rabbit medial collateral ligaments (MCL). Continuous and stepwise LDI scans were compared using correlation and linear regression analysis of image averages and standard deviations. Using the same method of analysis, LDI measurements using red and NIR lasers indicated a high degree of correlation, at least over the ranges of perfusion assessed, indicating that red and NIR lasers measure similar regions of flow in the rabbit MCL. These experiments confirm that both LDI techniques provide a valid in vivo measure of dynamic changes in connective tissue perfusion and could have significant impact on the understanding and treatment of joint injury and arthritis.     

Calcium-dependent regulation of the membrane potential and extrajunctional acetylcholine receptors of rat skeletal muscle

The resting membrane potential and the development of extrajunctional acetylcholine receptors were measured in strips of rat diaphragm muscle that had been cultured for 48 h. The resting membrane potential fell and the density of extrajunctional acetylcholine receptors increased during this period. The addition of the divalent ionophore A23187 to the culture medium inhibited these changes. The maximal effective concentration of A23187 was 1.0 μm. At this concentration the ionophore inhibited the fall in membrane potential by 12.0 mV and the increase in extrajunctional acetylcholine receptor development by 61%. The ionophore was also effective in partially restoring these properties in muscles that had been denervated for 3 days prior to culturing. The actions of A23187 required the presence of calcium. The effects of A23187 were similar to inhibitors of protein and ribonucleic acid synthesis, although its effect on acetylcholine receptor development was greater than its effect on overall protein synthesis (23–36% inhibition). Caffeine (5 mm) was also effective in inhibiting the changes in membrane properties of cultured denervated muscle: the membrane potential was raised 6.2 mV and extrajunctional acetylcholine receptor development was inhibited by 40%. Dibutyryl guanosine cyclic 3',5'-monophosphate at concentrations of 0.2 and 1.0 mm had no significant effect on the membrane potential or extrajunctional acetylcholine receptor development of cultured denervated muscle. Similar concentrations of dibutyryl adenosine cyclic 3',5'-monophosphate raised the membrane potential but had little effect on the development of extrajunctional acetylcholine receptors.Of the agents tested, only the divalent ionophore A23187 or caffeine inhibited the fall in membrane potential and the increase in extrajunctional acetylchonine receptors that occurred in cultured muscles. Both A23187 annd caffeine are known to elevate cytoplasmic levels of calcium ions. Since contractile activity prevents denervation-induced changes in muscle and is associated with a rise in the free intracellular calcium ion concentration, it is suggested that its effects on the regulation of the resting membrane potential and the development of extrajunctional acetylcholine receptors may be exerted through cytoplasmic calcium ions.     

Hypothalamic monoamines measured by microdialysis in rats treated with 2-deoxy-glucose or d-fenfluramine

The effects on brain monoamines (norepinephrine, serotonin and the metabolite of dopamine) following administration of d-fenfluramine (10 mg/kg IP) and 2-deoxy-d-glucose (500 mg/kg IP) have been measured by microdialysis from the ventromedial hypothalamus, lateral hypothalamic area and dorsomedial hypothalamus of conscious, unrestrained rats. Following administration of d-fenfluramine there was a significant increase in the concentration of serotonin in the ventromedial hypothalamus and lateral hypothalamic area, but no significant increase in the DMH. 5-HIAA (5-hydroxy-3-indoleacetic acid), the metabolite of serotonin, was increased in the DMH, but not in the other two regions. DOPAC (3,4-dihydroxyphenylacetic acid) was increased following fenfluramine treatment in all three regions examined. An increase in norepinephrine was observed in the VMH, but not in the other two regions, while the concentration of the 3-methoxy-4-hydroxyphenylglycol (MHPG) was increased in both areas. Treatment with 2-deoxy-D-glucose (2DG) was associated with fewer changes. In the lateral hypothalamic area there was a decrease in 5-HIAA and an increase in DOPAC. In the VMH there was an increase in norepinephrine and a decrease in MHPG in the DMH, but otherwise no significant alterations were observed.(ABSTRACT TRUNCATED AT 250 WORDS)     

Sexual harassment: how should management handle it?

Sexual harassment is against the law and can place health care facilities at substantial risk in lawsuits as well as disrupt their caring and professional atmosphere. In some cases, health care facilities are held responsible for nonemployees' harassment of employees, as well as for harassment by employees. In addition, if an employee receives benefits such as a promotion in exchange for sexual favors, the organization may be liable for discrimination against persons who did not receive such benefits. The Equal Employment Opportunity Commission has established guidelines for identifying and redressing instances of sexual harassment. They instruct health care facilities to issue a policy statement explaining to employees the institution's opposition to sexual harassment and outlining procedures for lodging a complaint. It is strongly recommended that health care facilities: Investigate complaints thoroughly, tactfully, and evenhandedly. Establish a progressive discipline schedule and administer it consistently to all employees. Document the investigatory and decision making process.