Schwann cells responding to primary demyelination in vivo express p75NTR and c-erbB receptors: a light and electron immunohistochemical study.

We have used quantitative and qualitative light microscope immunohistochemistry to examine the expression of p75NTR and c-erbB receptors in Schwann cells in a demyelinating lesion induced by the intraneural injection of lysophosphatidyl choline (LPC). We report that levels of p75NTR, c-erbB2 and c-erbB4, as assessed using image analysis of immuno-peroxidase labelled sections, and c-erbB3, as assessed by eye, increased within each lesion site soon after the initiation of myelinolysis, peaked between 5 and 8 days after induction of demyelination and fell to undetectable levels at the onset of remyelination. Pre-embedding immunoelectron microscopy confirmed that Schwann cells ensheathing demyelinated axons were p75NTR positive. Immunolabel decorated overlapping processes of neighbouring Schwann cells, suggesting that in this context p75NTR could play a role in juxtacrine signalling between reacting cells. We conclude that upregulation of p75NTR and c-erbB receptors is a constitutive Schwann cell response to an acute disruption of the axon-Schwann cell relationship.

An immuno-electronmicroscopical study of the distribution of laminin within autografts of denatured muscle.

We have used an immunogold post-embedding technique to examine, qualitatively and quantitatively, the distribution of laminin along sarcolemmal basal laminae of variously treated muscle autografts placed in transected rat sciatic nerves. We found that freeze-thawing or heating to 60 degrees C prior to grafting did not affect laminin labelling density along the sarcolemmal basal laminae, either at the time of preparation or 7 days after grafting. In sharp contrast, heating to 80 degrees C significantly reduced laminin labelling density. These findings are consistent with our earlier work showing that frozen-thawed or 60 degrees C muscle autografts both support axonal regeneration, whereas 80 degrees C grafts do not, and add further support to the view that laminin is a functionally important molecule in nerve regeneration. We have compared immunostaining using 10 nm gold particles with silver enhancement of 5 nm gold particles: although labelling density was higher in the silver-enhanced preparations, there was no increase in background labelling. Although empty sarcolemmal basal lamina tubes were frequently highly infolded, there was no evidence of preferential labelling of either 'peaks' or 'troughs' of the infolded basal laminae.

The changing medical student population at the University of Cape Town.

OBJECTIVE: Since 1981, the composition of applicants and students admitted to the medical school of the University of Cape Town has changed gradually. The objective of this paper is to quantify these changes and explore possible reasons for them. DESIGN: A retrospective analysis of the actual data accumulated at each annual intake was performed and the trends determined. SETTING: Only data for the University of Cape Town medical school were evaluated. Data published by similar institutions were used for comparative purposes. RESULTS: The number of applicants has risen steadily from 1,229 in 1981 to 2,330 in 1994, so that the applicant/admission ratio now stands at 12,1:1. During this same period, the percentage of women in the class has increased, with women outnumbering men in both 1992 and 1993. In 1994, black African students comprised 24% of those admitted to the M.B. Ch.B. programme, and of these 30.4% were women. By comparison, their white colleagues constituted 45.3% of the class, 57.5% of this cohort being women. CONCLUSIONS: The composition of the 1st-year M.B. Ch.B. class at the University of Cape Town has become multiracial in character, a factor achieved partly through academic support and affirmative action. The heterogeneity of the class, particularly in respect of gender, language and socio-economic factors, while appropriate and necessary, will have an impact on the university and the profession.

The distribution of astrocytes, oligodendroglia and myelin in normal and transplanted rat superior colliculus: an immunohistochemical study.

Immunohistochemical methods have been used to determine the distribution of macroglia and myelin in the normal rat superior colliculus (SC) and in grafts of fetal tectal tissue. The fetal tissue was derived from 15 day-old (E15) rat embryos and was transplanted onto the midbrain of newborn host rats of the same (PVG/c) strain. Antibodies to glial fibrillary acidic protein (GFAP) and carbonic anhydrase II (CAII) were used to visualize astrocytes and oligodendroglia respectively. Myelin was immunostained with antibodies to either proteolipid protein (PLP) or myelin basic protein (MBP). In the normal SC, GFAP positive astrocytes were found scattered throughout the SC, particularly in the superficial layers. They were especially prominent at the pial surface, around major blood vessels and at the midline between the two colliculi. CAII immunoreactive oligodendroglia and associated myelin were also found throughout the SC; by far the lowest density was seen in the stratum griseum superficiale (SGS). Both types of macroglia cell were found in abundance in tectal transplants, indicating that the precursors of these glial types were present in the E15 rat mesencephalon. In mature grafts, large numbers of fibrous astrocytes were found throughout the neuropil and the level of GFAP immunoreactivity was consistently greater than in host SC. Astrocytes seemed to be maintained in a reactive, perhaps immature state within the grafted tissue. Tectal transplants possessed large numbers of fully differentiated CAII-positive oligodendroglia and the grafts contained a dense network of myelinated axons. However the distribution of CAII and PLP immunoreactivity was not homogeneous; there were localized, well-defined regions that contained few oligodendroglia and relatively little myelin. These areas stained intensely for acetylcholinesterase (AChE) and were almost certainly homologous to the SGS of normal SC. The relative lack of oligodendroglia in the AChE stained patches in grafts and in SGS in situ suggests that local factors influencing the proliferation and distribution of oligodendroglia in normal SC may have been operating in a similar manner within the tectal transplant neuropil.

Filtration of shed mediastinal blood.

Re-infusion of shed blood carries the risk of re-infusing cellular debris. All re-infusion devices have some sort of integral filtration which is variably supplemented with a second intravenous filter. Using electron microscopy we have observed what debris is collected by secondary filtration. In 12 patients studied, nine out of 12 filters had significant amounts of cellular debris present, but not clearly related to increased rates of postoperative bleeding. Noncellular debris, silicon and strands of cellulose were also observed. Although we have not detected any clinically significant embolic phenomena from re-infusion of shed mediastinal blood, it seems prudent to include a second filter prior to re-infusion.

Electron microscopic immunocytochemistry of GAP-43 within proximal and chronically denervated distal stumps of transected peripheral nerve.

Growth-associated protein, GAP-43 was initially described as a neuron-specific molecule thought to play a critical role in axonal growth and regeneration. However, it is also expressed in vitro in certain CNS glia, Schwann cell precursors and non-myelinating Schwann cells. In this paper, we report the subcellular localization of GAP-43 in vivo in chronically-denervated Schwann cells in the distal stumps of previously transected rat sciatic nerve. We have used a progressive lowering of temperature method combined with the non-polar acrylic resin Lowicryl HM20 and a post-embedding labelling regime to visualize the distribution of GAP-43, S-100 (marker for Schwann cells), RT97 and NF68 (markers for different subunits of the neurofilament molecule). We report that (1) the smallest calibre regrowing axons were GAP-43-positive, sometimes NF68-positive but always RT97-negative; (2) regenerating myelinated axons and larger unmyelinated axons (> 0.7 microns diameter) were NF68-positive, RT97-positive but GAP-43-negative; (3) cytoplasmic processes within Schwann cell basal lamina tubes in the distal stumps were S-100-positive, GAP-43-positive but RT97- and NF68-negative. The similar localization of GAP-43 within regrowing axons and denervated Schwann cells suggests that GAP-43 may function similarly in both situations, and may thus be involved in motility and/or elongation of axons and Schwann cells during regeneration.

The pharmacodynamics of alcuronium in the elderly.

Alcuronium (0.2 mg/kg) was given to 12 elderly patients, mean age 77 years (range 70-88 years) and 12 young patients, mean age 24 years (range 18-32 years) undergoing general anaesthesia. A compound muscle action potential was monitored continuously throughout anaesthesia, using an electromyograph and the train-of-four twitch technique. The rate of onset and maximum block achieved were similar in both the young and elderly patients, as were the times to 20% recovery of the first twitch compared with control (T1 : T0) and fourth twitch compared with the first, (T4 : T1). In contrast, the time to 70% recovery of T1 : T0 was significantly prolonged in the elderly (138 as compared with 89 minutes: p less than 0.01) as was the recovery index (25-75%) for T1 : T0 (95 as compared with 46 minutes: p less than 0.01) and the time to 70% recovery of T4 : T1 (181 as compared with 131 minutes: p less than 0.05). The recovery curves for T1 : T0 and T4 : T1 were also significantly different in the elderly from the young group (p less than 0.01 in both instances). These results show that the duration of action of alcuronium is significantly prolonged in the elderly.

The effect of benserazide on the peripheral and central distribution and metabolism of levodopa after acute and chronic administration in the rat.

1. The effects of levodopa alone (50 mg kg-1) and levodopa (10 mg kg-1) plus benserazide (50 mg kg-1) were tested on the levels of dopa, dopamine, 3-methoxytyrosine (3-MT), 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), measured by h.p.l.c. with electrochemical detection, in samples of plasma, CSF, urine, striatum and hypothalamus of rats taken 30 min after injection. Levodopa plus benserazide produced significantly higher levels of dopa in plasma and brain than levodopa alone and reduced the peripheral synthesis and metabolism of dopamine. 2. When given chronically over 6 weeks the advantages of adding benserazide (50 mg kg-1 day-1) to levodopa (40 mg kg-1 day-1) were less marked and although more dopamine was present in the striatum than with levodopa given alone (200 mg kg-1 day-1) there was no evidence of any increase in its metabolites (HVA and DOPAC) and therefore of its turnover and utilisation. 3. The most striking effect of chronic treatment with levodopa plus benserazide was the appearance of large quantities of 3-MT in plasma, CSF and brain. 4. When levodopa alone, or levodopa plus benserazide, was given as an acute challenge to animals receiving the same treatment chronically, it was found that levodopa alone still produced increases in striatal dopamine, DOPAC and HVA in those animals dosed chronically on levodopa, but it was less effective in this respect when given with benserazide to the animals dosed with levodopa plus benserazide. 5. It is concluded that this difference in levodopa distribution may depend on the persistence in benserazide-treated animals of 3-MT, which has a long half-life and may compete with dopa for transport into the blood and brain. 6. The implication of these findings to the treatment of Parkinsonism is discussed.

Use of enoximone in weaning from cardiopulmonary bypass following mitral valve surgery.

Mitral valve surgery is often complicated by a postoperative low cardiac output state. In addition, some patients may have pre-existing pulmonary hypertension. Conventional inotropes, such as dopamine and dobutamine, tend to increase pulmonary vascular resistance. However, enoximone has both inotropic and vasodilatory properties. Ten patients, who had undergone mitral valve surgery and in whom weaning from cardiopulmonary bypass was unsuccessful without inotropic support, were treated with enoximone, 1 mg/kg loading dose plus 10 micrograms/kg/min continuous infusion, to assist in weaning from bypass. A significant and sustained increase in cardiac index was achieved without an increase in heart rate. At the same time, mean arterial pressure, systemic vascular and pulmonary vascular resistances were significantly decreased.

Pharmacokinetics of atracurium and laudanosine in the elderly.

The pharmacokinetics of a bolus dose of atracurium 0.6 mg kg-1 and its metabolite laudanosine were studied in 11 elderly (mean age 80.9 yr) and 10 young patients (mean age 23.8 yr) undergoing elective surgery. The elimination half-life (T1/2 beta) of atracurium was significantly longer in the elderly group (23.1 v. 20.1 min), but there was no significant difference between the two groups in clearance (Cl), the volume of distribution (V beta) or the mean residence time (MRT) of atracurium. Laudanosine T1/2 beta was also significantly longer (229.1 v. 173.1 min) and the clearance significantly slower (4.85 v. 7.29 ml min-1 kg-1) in the elderly. There was, however, no significant difference in V beta for laudanosine between the two groups. These data suggest that atracurium depends to a small extent on the liver or the kidney for its metabolism and excretion, and that, as these routes of excretion are less efficient in the elderly, T1/2 beta is prolonged in this age group. The deteriorating function of these organs with increasing age may also explain the altered pharmacokinetics of laudanosine.

The pharmacokinetics and clinical effects of a low dose of alfentanil in elderly patients.

Alfentanil is a potent short-acting opioid analgesic which depresses respiration and can cause cardiovascular depression. The elderly can show greater sensitivity to opioid drugs which may be related to pharmacokinetic differences. The pharmacokinetics and clinical effects of alfentanil were studied in 10 elderly patients aged 68-86 years who were undergoing cystoscopy or urethrotomy under general anesthesia. After induction with thiopentone, and while the patient was breathing nitrous oxide with halothane 0.5% (enflurane 1.0% was given to one patient), a dose of alfentanil 4 micrograms/kg was given 15, 20, 30, 45 and 60 minutes after the alfentanil administration, and then every 30 minutes for 6 hours. Pulse rate (PR), systolic blood pressure (SBP), and minute volume (MV, calculated from the respiratory rate and the tidal volume) were measured at 1, 3, 5, 7 and 9 minutes after the alfentanil injection. Pharmacokinetic analysis showed Vc 82 (+/- S.D. 26) ml/kg; VDSS 277 (+/- S.D. 71) ml/kg; clearance 2.01 (+/- S.D. 0.64) ml/kg/min; t1/2 beta 117 (+/- S.D. 24) min. Comparison of these results with the results of other studies supports the view that older patients eliminate alfentanil less rapidly than younger patients, with prolongation of t1/2 beta and decreased clearance. The clinical results showed a decrease in minute volume from a mean value of 5944 ml before alfentanil to 1240 ml 1 minute after alfentanil (P less than 0.001). The minute volume was still significantly lower at 3 and 5 minutes, but had returned to the pre-alfentanil value by 7 minutes.(ABSTRACT TRUNCATED AT 250 WORDS)